Marine electric heating control circuit and control method thereof

Abstract

The invention relates to a marine electric heating control circuit, which comprises an electric heating circuit and a fan circuit which are connected in parallel on a control power supply, and is characterized in that the fan circuit comprises a fan thermal relay, a local fan stop button, a local fan start button and a fan contactor which are sequentially connected in series; on the electric heating circuit, one end of a control power supply is sequentially connected in series with a second normally open switch of a fan contactor, a manual-automatic change-over switch is connected back to the other end of the control power supply through a manual circuit, an automatic circuit and a delay circuit, and the manual circuit is respectively connected with a first-gear motor thermal contactor, a second-gear motor thermal contactor and a third-gear motor thermal contactor by adopting a first-stage manual circuit, a second-stage manual circuit and a third-stage manual circuit which are connected in parallel; the automatic circuit comprises a first-level automatic circuit, a second-level automatic circuit and a third-level automatic circuit which are connected in parallel, and the automatic circuit is connected with a first-level motor thermal contactor, a second-level motor thermal contactor and a third-level motor thermal contactor through a third-level temperature controller temperature control The circuit control can meet the requirements of automatic and manual mode electric heating switching, multi-gear grading starting, safe and stable gear shifting and fan shutdown delay.

Description

Technical Field

[0001] The invention relates to an electric heating technology, in particular to a control circuit and a control method of a marine electric heating. Background Art

[0002] With the development of ship technology, the humanization requirements for marine auxiliary equipment are increasing day by day. The existing control of marine electric heating and fans has always been a difficult problem for marine air conditioners and heaters. There are the following problems: the thermostat is damaged in automatic mode and the electric heating cannot be turned on; when the electric heating is damaged in automatic mode, it is impossible to judge and put the next gear into use; the electric heating power is large and it impacts the power grid when it is started at the same time; after the electric heating and fan are stopped at the same time, there is heat that cannot be sent out. The above problems directly restrict the safe and stable use of marine electric heating and fans. Summary of the invention

[0003] The present invention provides a control circuit and a control method for marine electric heating which can take into account automatic and manual mode electric heating switching, multi-speed graded starting, safe and stable gear shifting and delayed fan shutdown.

[0004] The technical scheme adopted by the present invention is: a control circuit of marine electric heating, comprising an electric heating circuit and a fan circuit connected in parallel to a control power supply, characterized in that: the fan circuit comprises a fan thermal relay, a local fan stop button, a local fan start button and a fan contactor connected in series in sequence, and the local fan start button is connected in parallel with the first normally open switch of the fan contactor; the second normally open switch of the fan contactor and the manual-automatic conversion switch are connected in series in sequence from one end of the control power supply to the electric heating circuit, the manual contact of the manual-automatic conversion switch is connected back to the other end of the control power supply via a manual circuit, and the automatic contacts of the manual-automatic conversion switch are connected back to the other end of the control power supply via an automatic circuit and an automatic intermediate relay, respectively, the manual circuit comprises a first-level, a second-level and a third-level manual circuit in parallel, the first-level manual circuit is connected in series with the first-level manual opening knob of the electric heating, the first-level normally closed switch of the automatic intermediate relay, and the first-level electric heating contactor, the first-level intermediate relay is connected in parallel to the first-level electric heating contactor, the second-level manual opening button, the second-level normally closed switch of the automatic intermediate relay, and the second-level electric heating contactor are connected in series to the second-level manual circuit, and the second-level electric heating contactor is connected in parallel to the second-level manual circuit. A two-level intermediate relay is connected in series, and the third-level manual circuit is connected in series with the electric heating third-level manual opening knob, the automatic intermediate relay three-level normally closed switch, and the third-level electric heating contactor. The automatic circuit includes a first-level, a second-level, and a third-level automatic circuit in parallel. The first-level automatic circuit is connected in series with the first-level temperature control switch of the three-level temperature controller and the first-level normally open switch of the automatic intermediate relay. The second-level automatic circuit is connected in series with the first-level intermediate relay normally open delay switch, the second-level temperature control switch of the three-level temperature controller, and the second-level normally open switch of the automatic intermediate relay. The first-level intermediate relay normally open delay switch and the second-level temperature control switch of the three-level temperature controller are connected in parallel with the first-level electric heating contactor normally open delay switch and the first temperature controller normally open switch connected in series in sequence. The three-level automatic circuit is connected in series with the second-level intermediate relay normally open delay switch, the third-level temperature control switch of the three-level temperature controller, and the three-level normally open switch of the automatic intermediate relay. The second-level intermediate relay normally open delay switch and the third-level temperature control switch of the three-level temperature controller are connected in parallel with the second-level electric heating contactor normally open delay switch and the second temperature controller normally open switch connected in series in sequence. The three-level temperature controller is arranged at the air supply outlet.

[0005] It also includes a delay circuit connected in parallel to the control power supply. The delay circuit is connected in parallel through the normally open switches of the first, second and third gear electric heating contactors and then connected to a delay relay. The normally open delay switch of the delay relay is connected in parallel to the local fan stop button and the local fan start button.

[0006] The electric heating circuit and the fan circuit are connected back to the other end of the control power supply through the electric heating body over-temperature protection switch and the external over-temperature insulation switch after electric heating.

[0007] The first-level, second-level and third-level normally closed switches of the automatic intermediate relay are interlocked with the first-level, second-level and third-level normally open switches of the automatic intermediate relay.

[0008] The setting temperature of the normally open switch of the first temperature controller is consistent with that of the first temperature control switch of the three-stage temperature controller, and the setting temperature of the normally open switch of the second temperature controller is consistent with that of the second temperature control switch of the three-stage temperature controller.

[0009] The fan circuit is also connected in series with a local fan emergency stop button.

[0010] A control method for marine electric heating, characterized in that: a. Fan start: Press the local fan start button, connect the fan circuit when the fan thermal relay switch is closed, and the fan contactor is energized to start the fan. At this time, the first and second normally open switches of the fan contactor are closed, locking the local fan start button to connect the fan circuit in the energized state; b. Manual electric heating start: The manual-automatic conversion switch is switched to the manual contact. When the over-temperature protection switch of the electric heating body and the external over-temperature insulation switch after the electric heating are closed, the first, second and third gear manual start knobs of the electric heating are opened respectively as needed, and the first, second and third gear manual circuits are connected respectively, and the first, second and third gear electric heating contactors are started; c. Automatic electric heating start: The manual-automatic conversion switch is switched to the automatic contact, the automatic intermediate relay is energized, the first-level, second-level, and third-level normally closed switches of the automatic intermediate relay are interlocked with the first-level, second-level, and third-level normally open switches of the automatic intermediate relay to open and close respectively, and the manual circuit is always in a disconnected state; when the temperature of the air supply outlet is lower than the set air outlet temperature according to the three-level temperature controller, the first-level temperature control switch of the three-level temperature controller is closed, the first-level automatic circuit is connected, the first-level electric heating contactor is energized, the first-level electric heating is turned on to start heating, and the first-level intermediate relay is energized at the same time; when the normally open delay switch of the first-level intermediate relay still fails to reach the set temperature of the three-level temperature controller within the delay time of the first-level electric heating start, the second-level automatic circuit is connected, the second-level electric heating contactor is energized, the second-level electric heating is turned on to start heating, and the third-level temperature is reached within the delay time of the first-level electric heating start The controller sets the temperature, the first-level temperature control switch of the three-level temperature controller is disconnected, the first-level electric heating contactor normally open delay switch is delayed to engage, and the first temperature controller normally open switch is engaged. At this time, the second-level electric heating contactor can remain energized and continue to heat on demand; at the same time, the second-level intermediate relay is energized, and the second-level intermediate relay normally open delay switch still cannot reach the set temperature of the three-level temperature controller within the delay time of the second-level electric heating device, then the three-level automatic circuit is connected, the third-level electric heating contactor is energized, and the third-level electric heating device is turned on to start heating, and the electric heating is turned on and heated in each gear; the set temperature of the three-level temperature controller is reached within the delay time of the second-level electric heating device, the first-level temperature control switch of the three-level temperature controller is disconnected, the second-level electric heating contactor normally open delay switch is delayed to engage, and the second temperature controller normally open switch is engaged. At this time, the third-level electric heating contactor can remain energized and continue to heat on demand; d. Electric heating protection shutdown: When the over-temperature protection switch of the electric heating body or the external over-temperature insulation switch after the electric heating is accidentally disconnected, the fan circuit and the electric heating circuit will lose power; e. Active shutdown: first switch the automatic contact of the manual-automatic conversion switch or reset the manual contact to disconnect the electric heating circuit, and then press the local fan stop button. When the manual-automatic conversion switch disconnects the electric heating circuit, the first, second and third gear electric heating contactors lose power, the first, second and third gear electric heating contactors normally open, the delay relay of the delay circuit disconnects and loses power, the normally open delay switch of the delay relay opens after a delay to disconnect the fan circuit, the fan contactor loses power, and the fan stops; f. Fan protection or emergency shutdown: The fan thermal relay is disconnected when the fan temperature is too high or the local fan emergency stop button is pressed, the fan circuit is disconnected, the fan contactor loses power, the second normally open switch of the fan contactor is disconnected, and the electric heating circuit is disconnected.

[0011] The beneficial effects of the present invention are: 1. When starting the work, by pressing the local fan start button, the fan contactor is energized, the first normally open switch of the fan contactor locks the inching local fan start button, and the second normally open switch of the fan contactor connects the electric heating circuit; at this time, the manual-automatic switch can be selected to switch to the manual contact or the automatic contact as needed to connect the automatic circuit and the manual circuit respectively. Under the manual circuit, the first, second and third gear manual opening knobs of the electric heating can be used to connect the first, second and third gear manual circuits respectively, so as to realize the manual selection and opening of the first, second and third gear electric heating contactors; under the automatic circuit, the three-level temperature The temperature controller monitors the temperature. When the set temperature of the three-stage temperature controller is not reached, the first-stage temperature control switch of the three-stage temperature controller is closed, the first-stage automatic circuit and the first-stage electric heating contactor are connected, and the first-stage electric heating starts heating. When the first-stage intermediate relay normally open delay switch still does not reach the set temperature of the three-stage temperature controller within the first-stage electric heating start delay time, the second-stage automatic circuit is connected, and the second-stage electric heating is started. Similarly, the third-stage electric heater is started later, which can meet the requirements of multi-stage electric heating in low temperature environment and high heating temperature requirements, and avoid excessive power impact on the ship power grid; 2. When the first-gear electric heating does not meet the temperature monitored by the first-level temperature control switch of the three-level temperature controller, the second-gear electric heating is heated for a period of time, and the temperature reaches the temperature monitored by the second-level temperature control switch of the three-level temperature controller, and the first and second-level temperature control switches of the three-level temperature controller are disconnected. At this time, the normally open delay switch of the first-gear electric heating contactor is closed, and the normally open switch of the first temperature controller is closed to ensure that the second-gear electric heating keeps heating; similarly, when the second-gear electric heating does not meet the temperature monitored by the second-level temperature control switch of the three-level temperature controller, the third-gear electric heating is heated for a period of time, and the temperature reaches the temperature monitored by the third-level temperature control switch of the three-level temperature controller, and the first, second, and third-level temperature control switches of the three-level temperature controller are disconnected. At this time, the normally open delay switch of the second-gear electric heating contactor is closed, and the normally open switch of the second temperature controller is closed to ensure that the third-gear motor heat keeps heating; it can be ensured that if the electric heating power of any gear is insufficient or damaged and the set temperature cannot be reached after working for a period of time, the next gear electric heating will be automatically switched to keep heating; 3. The first, second and third level normally closed switches of the automatic intermediate relay are interlocked with the first, second and third level normally open switches of the automatic intermediate relay, which can realize the safe and stable disconnection of the automatic line from the manual line, and the safe and stable disconnection of the automatic line under the manual line, which helps to improve the safety and stability of manual and automatic switching; 4. When the fan needs to be stopped, pressing the local fan stop button will not stop the fan directly. You need to first select the manual-automatic switch to switch to the empty position to disconnect the automatic and manual circuits, or manually open the knob of the first, second, and third gear electric heating to disconnect the first, second, and third-level manual circuits. After the first, second, and third gear electric heating contactors lose power, and the first, second, and third-level electric heating contactors normally open the delay circuit, the normally open delay switch of the delay relay opens with a delay to disconnect the fan circuit, ensuring that the fan is stably delayed to stop and discharge the residual electric heating heat in the equipment; 5. The over-temperature protection switch of the electric heating body corresponds to the first, second and third gear electric heating, monitors the local over-temperature protection of the electric heating, and can disconnect the circuit protection when any electric heating is over-temperature. The external over-temperature insulation switch after electric heating can monitor the temperature after the first, second and third gear electric heating to avoid over-temperature accidents when multiple gear electric heating works at the same time due to accidents of switches, relays and contactors in the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the electrical diagram of the present invention.

[0013] In the figure: control power supply LN, fan thermal relay 1FR, local fan start button 1SB, local fan stop button 2SB\local fan emergency stop button 3SB, fan contactor 1KM, fan contactor first normally open switch 1KM-1, fan contactor second normally open switch 1KM-2, delay relay 1KT, delay relay normally open switch 1KT-1, manual-automatic switching switch SA, electric heating first gear manual opening knob 1SS, electric heating second gear manual opening knob 2SS, electric heating third gear manual opening knob 3SS, first gear electric heating contactor 2KM, first gear electric heating contactor normally open switch 2KM-1, first gear electric heating contactor normally open delay switch 2KM-2, second gear electric heating contactor 3KM, second gear electric heating contactor normally open switch 3KM-1, second gear electric heating contactor normally open delay switch 3KM-2, third gear electric heating contactor 4KM, first-level intermediate relay Electrical appliances 2KT, first-level intermediate relay normally open delay switch 2KT-1, second-level intermediate relay 3KT, second-level intermediate relay normally open delay switch 3KT-1, automatic intermediate relay 15KA, automatic intermediate relay first-level normally closed switch 15KA-1, automatic intermediate relay second-level normally closed switch 15KA-2, automatic intermediate relay third-level normally closed switch 15KA-3, automatic intermediate relay first-level normally open switch 15KA-4, automatic intermediate relay second-level normally open switch 15KA-5, automatic intermediate relay third-level normally open switch 15KA-6, three-level temperature controller first-level temperature control switch 1ST-1, three-level temperature controller second-level temperature control switch 1ST-2, three-level temperature controller third-level temperature control switch 1ST-3, first temperature controller normally open switch 2ST, second temperature controller normally open switch 3ST, electric heating body over-temperature protection switch CW, external over-temperature insulation switch 4ST after electric heating. DETAILED DESCRIPTION

[0014] The following is a further description with reference to the accompanying drawings.

[0015] Figure 1As shown: a control circuit for marine electric heating, including control power supply LN, fan thermal relay 1FR, local fan start button 1SB, local fan stop button 2SB\local fan emergency stop button 3SB, fan contactor 1KM, fan contactor first normally open switch 1KM-1, fan contactor second normally open switch 1KM-2, delay relay 1KT, delay relay normally open switch 1KT-1, manual-automatic switching switch SA, electric heating first gear manual opening knob 1SS, electric heating second gear manual opening knob 2SS, electric heating third gear manual opening knob 3SS, first gear electric heating contactor 2KM, first gear electric heating contactor normally open switch 2KM-1, first gear electric heating contactor normally open delay switch 2KM-2, second gear electric heating contactor 3KM, second gear electric heating contactor normally open switch 3KM-1, second gear electric heating contactor normally open delay switch 3KM-2, third gear electric heating contactor 4 KM, first-level intermediate relay 2KT, first-level intermediate relay normally open delay switch 2KT-1, second-level intermediate relay 3KT, second-level intermediate relay normally open delay switch 3KT-1, automatic intermediate relay 15KA, automatic intermediate relay first-level normally closed switch 15KA-1, automatic intermediate relay second-level normally closed switch 15KA-2, automatic intermediate relay third-level normally closed switch 15KA-3, automatic intermediate relay first-level normally open switch 15KA-4, automatic intermediate relay second-level normally open switch 15KA-5, automatic intermediate relay third-level normally open switch 15KA-6, three-level temperature controller first-level temperature control switch 1ST-1, three-level temperature controller second-level temperature control switch 1ST-2, three-level temperature controller third-level temperature control switch 1ST-3, first temperature controller normally open switch 2ST, second temperature controller normally open switch 3ST, electric heating body over-temperature protection switch CW, external over-temperature insulation switch 4ST after electric heating.

[0016] One end of the control power supply LN is connected back to the other end of the control power supply through the parallel electric heating circuit, fan circuit and delay circuit, and then through the electric heating body over-temperature protection switch CW and the external over-temperature insulation switch 4ST after electric heating.

[0017] The fan circuit includes a fan thermal relay 1FR, a local fan emergency stop button 3SB, a local fan stop button 2SB, a local fan start button 1SB and a fan contactor 1KM which are connected in series in sequence. The local fan start button 1SB is connected in parallel with a first normally open switch 1KM-1 of the fan contactor; In the electric heating circuit, one end of the control power supply LN is connected in series with the second normally open switch 1KM-2 of the fan contactor and the manual-automatic conversion switch SA. The manual contacts of the manual-automatic conversion switch SA are connected back to the other end of the control power supply through the manual line, and the automatic contacts of the manual-automatic conversion switch are connected back to the other end of the control power supply through the automatic line and the automatic intermediate relay 15KA. The manual circuit includes parallel first-level, second-level and third-level manual circuits. The first-level manual circuit is connected in series with the first-gear manual opening knob 1SS of electric heating, the first-level normally closed switch 15KA-1 of the automatic intermediate relay, and the first-gear electric heating contactor 2KM. The first-gear electric heating contactor 2KM is connected in parallel with the first-level intermediate relay 2KT. The second-level manual circuit is connected in series with the second-level manual opening button 2SS, the second-level normally closed switch 15KA-2 of the automatic intermediate relay, and the second-gear electric heating contactor 3KM. The second-level intermediate relay 3KT is connected in parallel with the second-gear electric heating contactor 3KM. The third-level manual circuit is connected in series with the third-level manual opening knob 3SS of electric heating, the third-level normally closed switch 15KA-3 of the automatic intermediate relay, and the third-gear electric heating contactor 4KM. The automatic circuit includes the first-level, second-level and third-level automatic circuits connected in parallel. The first-level automatic circuit is connected in series with the first-level temperature control switch 1ST-1 of the three-level temperature controller and the first-level normally open switch 15KA-4 of the automatic intermediate relay. The second-level automatic circuit is connected in series with the first-level intermediate relay normally open delay switch 2KT-1, the second-level temperature control switch 1ST-2 of the three-level temperature controller and the second-level normally open switch 15KA-5 of the automatic intermediate relay. The first-level intermediate relay normally open delay switch and the second-level temperature control switch of the three-level temperature controller are connected in parallel with the first-speed electric heating contactor normally open delay switch 2KM-2 and the first temperature controller normally open switch 2ST connected in series in sequence. The three-level automatic circuit The normally open delay switch 3KT-1 of the secondary intermediate relay, the three-stage temperature control switch 1ST-3 of the three-stage temperature controller, and the three-stage normally open switch 15KA-6 of the automatic intermediate relay are connected in series on the road. The normally open delay switch of the secondary intermediate relay and the three-stage temperature control switch of the three-stage temperature controller are connected in parallel with the normally open delay switch 3KM-2 of the second-stage electric heating contactor and the normally open switch 3ST of the second temperature controller in series. The setting temperature of the normally open switch of the first temperature controller is consistent with the first-stage temperature control switch of the three-stage temperature controller, and the setting temperature of the normally open switch of the second temperature controller is consistent with the second-stage temperature control switch of the three-stage temperature controller; the three-stage temperature controller is set at the air supply outlet. The normally closed switches of the first, second and third levels of the automatic intermediate relay are interlocked with the normally open switches of the first, second and third levels of the automatic intermediate relay.

[0018] The delay circuit is connected in parallel through the first, second and third electric heating contactor normally open switches 2KM-1, 3KM-1 and 4KM-1 and then connected to the delay relay 1KT. The delay relay normally open delay switch 1KT-1 is connected in parallel to the local fan stop button and the local fan start button.

[0019] A control method for marine electric heating, characterized in that: a. Fan start: Press the local fan start button, connect the fan circuit when the fan thermal relay switch is closed, and the fan contactor is energized to start the fan. At this time, the first and second normally open switches of the fan contactor are closed, locking the local fan start button to connect the fan circuit in the energized state; b. Manual electric heating start: The manual-automatic conversion switch is switched to the manual contact. When the over-temperature protection switch of the electric heating body and the external over-temperature insulation switch after the electric heating are closed, the first, second and third gear manual start knobs of the electric heating are opened respectively as needed, and the first, second and third gear manual circuits are connected respectively, and the first, second and third gear electric heating contactors are started; c. Automatic electric heating start: The manual-automatic conversion switch is switched to the automatic contact, the automatic intermediate relay is energized, the first-level, second-level, and third-level normally closed switches of the automatic intermediate relay are interlocked with the first-level, second-level, and third-level normally open switches of the automatic intermediate relay to open and close respectively, and the manual circuit is always in a disconnected state; when the temperature of the air supply outlet is lower than the set air outlet temperature according to the three-level temperature controller, the first-level temperature control switch of the three-level temperature controller is closed, the first-level automatic circuit is connected, the first-level electric heating contactor is energized, the first-level electric heating is turned on to start heating, and the first-level intermediate relay is energized at the same time; when the normally open delay switch of the first-level intermediate relay still fails to reach the set temperature of the three-level temperature controller within the delay time of the first-level electric heating start, the second-level automatic circuit is connected, the second-level electric heating contactor is energized, the second-level electric heating is turned on to start heating, and the third-level temperature is reached within the delay time of the first-level electric heating start The controller sets the temperature, the first-level temperature control switch of the three-level temperature controller is disconnected, the first-level electric heating contactor normally open delay switch is delayed to engage, and the first temperature controller normally open switch is engaged. At this time, the second-level electric heating contactor can remain energized and continue to heat on demand; at the same time, the second-level intermediate relay is energized, and the second-level intermediate relay normally open delay switch still cannot reach the set temperature of the three-level temperature controller within the delay time of the second-level electric heating device, then the three-level automatic circuit is connected, the third-level electric heating contactor is energized, and the third-level electric heating device is turned on to start heating, and the electric heating is turned on and heated in each gear; the set temperature of the three-level temperature controller is reached within the delay time of the second-level electric heating device, the first-level temperature control switch of the three-level temperature controller is disconnected, the second-level electric heating contactor normally open delay switch is delayed to engage, and the second temperature controller normally open switch is engaged. At this time, the third-level electric heating contactor can remain energized and continue to heat on demand; d. Electric heating protection shutdown: When the over-temperature protection switch of the electric heating body or the external over-temperature insulation switch after the electric heating is accidentally disconnected, the fan circuit and the electric heating circuit will lose power; e. Active shutdown: first switch the automatic contact of the manual-automatic conversion switch or reset the manual contact to disconnect the electric heating circuit, and then press the local fan stop button. When the manual-automatic conversion switch disconnects the electric heating circuit, the first, second and third gear electric heating contactors lose power, the first, second and third gear electric heating contactors normally open, the delay relay of the delay circuit disconnects and loses power, the normally open delay switch of the delay relay opens after a delay to disconnect the fan circuit, the fan contactor loses power, and the fan stops; f. Fan protection or emergency shutdown: The fan thermal relay is disconnected when the fan temperature is too high or the local fan emergency stop button is pressed, the fan circuit is disconnected, the fan contactor loses power, the second normally open switch of the fan contactor is disconnected, and the electric heating circuit is disconnected.

Claims

1. A control circuit for marine electric heating, comprising an electric heating circuit and a fan circuit connected in parallel to a control power supply, characterized in that: The fan circuit includes a fan thermal relay, a local fan stop button, a local fan start button and a fan contactor connected in series in sequence, and the local fan start button is connected in parallel with the first normally open switch of the fan contactor; the electric heating circuit is connected in series with the second normally open switch of the fan contactor and the manual-automatic conversion switch at one end of the control power supply, the manual contact of the manual-automatic conversion switch is connected back to the other end of the control power supply via a manual circuit, and the automatic contacts of the manual-automatic conversion switch are connected back to the other end of the control power supply via an automatic circuit and an automatic intermediate relay respectively. The manual circuit includes a primary, a secondary and a tertiary manual circuit in parallel, the primary manual circuit is connected in series with the first-gear manual opening knob of the electric heating, the first-gear normally closed switch of the automatic intermediate relay, and the first-gear electric heating contactor, the first-gear electric heating contactor is connected in parallel with the primary intermediate relay, the secondary manual circuit is connected in series with the second-gear manual opening button, the second-gear normally closed switch of the automatic intermediate relay, and the second-gear electric heating contactor, the second-gear electric heating contactor is connected in parallel with the secondary intermediate relay, and the third-gear manual circuit is connected in series with the third-gear manual opening knob of the electric heating A start knob, an automatic intermediate relay three-stage normally closed switch, and a third-stage electric heating contactor. The automatic circuit includes a first-stage, a second-stage, and a third-stage automatic circuit connected in parallel. The first-stage automatic circuit is connected in series with a first-stage temperature control switch of a three-stage temperature controller and a first-stage normally open switch of an automatic intermediate relay. The second-stage automatic circuit is connected in series with a first-stage intermediate relay normally open delay switch, a second-stage temperature control switch of a three-stage temperature controller, and a second-stage normally open switch of an automatic intermediate relay. The first-stage intermediate relay normally open delay switch and the second-stage temperature control switch of the three-stage temperature controller are connected in parallel with a first-stage electric heating contactor normally open delay switch and a first temperature controller normally open switch connected in series in sequence. The third-stage automatic circuit is connected in series with a second-stage intermediate relay normally open delay switch, a third-stage temperature control switch of a three-stage temperature controller, and a third-stage normally open switch of an automatic intermediate relay. The second-stage intermediate relay normally open delay switch and the third-stage temperature control switch of the three-stage temperature controller are connected in parallel with a second-stage electric heating contactor normally open delay switch and a second temperature controller normally open switch connected in series in sequence. The three-stage temperature controller is arranged at the air supply outlet.

2. A control circuit for marine electric heating according to claim 1, characterized in that: It also includes a delay circuit connected in parallel to the control power supply. The delay circuit is connected in parallel through the normally open switches of the first, second and third gear electric heating contactors and then connected to a delay relay. The normally open delay switch of the delay relay is connected in parallel to the local fan stop button and the local fan start button.

3. A control circuit for marine electric heating according to claim 1, characterized in that: The electric heating circuit and the fan circuit are connected back to the other end of the control power supply through the electric heating body over-temperature protection switch and the external over-temperature insulation switch after electric heating.

4. A control circuit for marine electric heating according to claim 1, characterized in that: The first-level, second-level and third-level normally closed switches of the automatic intermediate relay are interlocked with the first-level, second-level and third-level normally open switches of the automatic intermediate relay.

5. A control circuit for marine electric heating according to claim 1, characterized in that: The setting temperature of the normally open switch of the first temperature controller is consistent with that of the first temperature control switch of the three-stage temperature controller, and the setting temperature of the normally open switch of the second temperature controller is consistent with that of the second temperature control switch of the three-stage temperature controller.

6. A control circuit for marine electric heating according to claim 1, characterized in that: The fan circuit is also connected in series with a local fan emergency stop button.

7. A control method for marine electric heating, characterized in that: a. Fan start: Press the local fan start button, connect the fan circuit when the fan thermal relay switch is closed, and the fan contactor is energized to start the fan. At this time, the first and second normally open switches of the fan contactor are closed, locking the local fan start button to connect the fan circuit in the energized state; b. Manual electric heating start: The manual-automatic conversion switch is switched to the manual contact. When the over-temperature protection switch of the electric heating body and the external over-temperature insulation switch after the electric heating are closed, the first, second and third gear manual start knobs of the electric heating are opened respectively as needed, and the first, second and third gear manual circuits are connected respectively, and the first, second and third gear electric heating contactors are started; c. Automatic electric heating start: The manual-automatic conversion switch is switched to the automatic contact, the automatic intermediate relay is energized, the first-level, second-level, and third-level normally closed switches of the automatic intermediate relay are interlocked with the first-level, second-level, and third-level normally open switches of the automatic intermediate relay to open and close respectively, and the manual circuit is always in a disconnected state; when the temperature of the air supply outlet is lower than the set air outlet temperature according to the three-level temperature controller, the first-level temperature control switch of the three-level temperature controller is closed, the first-level automatic circuit is connected, the first-level electric heating contactor is energized, the first-level electric heating is turned on to start heating, and the first-level intermediate relay is energized at the same time; when the normally open delay switch of the first-level intermediate relay still fails to reach the set temperature of the three-level temperature controller within the delay time of the first-level electric heating start, the second-level automatic circuit is connected, the second-level electric heating contactor is energized, the second-level electric heating is turned on to start heating, and the third-level temperature is reached within the delay time of the first-level electric heating start The controller sets the temperature, the first-level temperature control switch of the three-level temperature controller is disconnected, the first-level electric heating contactor normally open delay switch is delayed to engage, and the first temperature controller normally open switch is engaged. At this time, the second-level electric heating contactor can remain energized and continue to heat on demand; at the same time, the second-level intermediate relay is energized, and the second-level intermediate relay normally open delay switch still cannot reach the set temperature of the three-level temperature controller within the delay time of the second-level electric heating device, then the three-level automatic circuit is connected, the third-level electric heating contactor is energized, and the third-level electric heating device is turned on to start heating, and the electric heating is turned on and heated in each gear; the set temperature of the three-level temperature controller is reached within the delay time of the second-level electric heating device, the first-level temperature control switch of the three-level temperature controller is disconnected, the second-level electric heating contactor normally open delay switch is delayed to engage, and the second temperature controller normally open switch is engaged. At this time, the third-level electric heating contactor can remain energized and continue to heat on demand; d. Electric heating protection shutdown: When the over-temperature protection switch of the electric heating body or the external over-temperature insulation switch after the electric heating is accidentally disconnected, the fan circuit and the electric heating circuit will lose power; e. Active shutdown: first switch the automatic contact of the manual-automatic conversion switch or reset the manual contact to disconnect the electric heating circuit, and then press the local fan stop button. When the manual-automatic conversion switch disconnects the electric heating circuit, the first, second and third gear electric heating contactors lose power, the first, second and third gear electric heating contactors normally open, the delay relay of the delay circuit disconnects and loses power, the normally open delay switch of the delay relay opens after a delay to disconnect the fan circuit, the fan contactor loses power, and the fan stops; f. Fan protection or emergency shutdown: The fan thermal relay is disconnected when the fan temperature is too high or the local fan emergency stop button is pressed, the fan circuit is disconnected, the fan contactor loses power, the second normally open switch of the fan contactor is disconnected, and the electric heating circuit is disconnected.

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