A tank container heating system control circuit

Abstract

The utility model discloses a kind of tank heating system control circuit, including operation starting circuit, indicating circuit and monitoring control circuit, operation starting circuit parallel water pump circuit and electric heating circuit, indicating circuit realizes the comprehensive visual monitoring of power supply, equipment operation and fault state, monitoring control circuit adopts electric heating tube, water and triple temperature control mechanism of medium in tank, and cooperate multi-gear heating adjustment.Electric circuit realizes water pump positive and negative rotation automatic switching by phase sequence relay, with short-circuit, overload, over-temperature protection and fault reset function, ensure that medium in tank is heated stably, improve system operation reliability and energy utilization efficiency.

Description

Technical Field

[0001] This utility model relates to a control circuit, specifically a control circuit for a tank heating system. Background Technology

[0002] With the rapid development of the modern logistics and transportation industry, tank containers, as a highly efficient medium transport carrier, are widely used in chemical, food, and pharmaceutical fields. The temperature stability of the medium carried inside directly affects the transport quality and safety. To meet the temperature control requirements of the medium inside the tank container, tank container heating systems have emerged. However, existing heating system control circuits have many shortcomings: First, the forward and reverse rotation control of the water pump relies on manual intervention, and abnormal phase sequence can easily lead to reverse operation of the water pump, affecting the heating cycle efficiency; Second, the electric heating operating status and fault information lack comprehensive visual monitoring, making it difficult to quickly locate the problem after a fault occurs; Third, the temperature control accuracy is insufficient, and a single temperature control link cannot simultaneously meet the multiple requirements of electric heating tube safety, outlet water temperature, and tank medium temperature; Fourth, the electric heating level switching flexibility is poor, making it impossible to adjust the load conditions according to actual heating needs, resulting in energy waste; Fifth, there is a lack of an effective reset mechanism after an over-temperature fault, which can easily lead to repeated abnormal operation of the equipment, affecting system reliability. Summary of the Invention

[0003] This invention provides a control circuit for a tank heating system that features precise control, safety protection, and status visualization, thereby overcoming the shortcomings of existing technologies.

[0004] The technical solution adopted by this utility model is: a control circuit for a tank heating system, including a start-up circuit, an indicator circuit, and a monitoring and control circuit, characterized in that: the start-up circuit includes an AC power supply, and a water pump circuit and an electric heating circuit are connected in parallel to the AC power supply.

[0005] The water pump circuit includes a water pump circuit breaker, a motor starter, and a water pump connected in series; the electric heating circuit includes an electric heating circuit breaker, an AC contactor, and an electric heater connected in series. The indicating circuit and monitoring control circuit are connected in parallel to the control power supply. The indicating circuit includes a pump indicating circuit, an electric heating operation circuit, and an electric heating fault indicating circuit, all connected in parallel to the control power supply. The pump indicating circuit is split into two parallel paths after passing through a bidirectional contact switch of the motor starter; one path carries a pump start indicator light, and the other carries a pump fault indicator light. The electric heating operation circuit is formed by connecting a normally open contact switch of an electric heating relay in parallel and then connecting it in series with the electric heating operation indicator light. The electric heating fault indicating circuit is formed by connecting a normally closed contact switch of an electric heating circuit breaker in parallel and then connecting it in series with the motor thermal fault indicator light. The monitoring control circuit includes an electric heating temperature relay connected in parallel to the control power supply. The hot water thermostat, the tank thermostat, the electric heating temperature relay, the hot water thermostat, and the tank thermostat are all externally connected to temperature sensors. The input terminal of the electric heating temperature relay's bidirectional contact switch is connected to the signal output terminal between the motor starter's bidirectional contact switch and the pump start indicator light. One side of the output terminal of the electric heating temperature relay's bidirectional contact switch is in contact with the signal output terminal, which is connected to the negative terminal of the control power supply via the over-temperature alarm indicator light. The other side of the output terminal of the electric heating temperature relay's bidirectional contact switch is connected sequentially to the normally closed switch inside the tank thermostat, the normally closed switch inside the hot water thermostat, the electric heating switch, the electric heating circuit breaker switch, and the electric heating relay connected to the negative terminal of the control power supply.

[0006] A control circuit for a tank heating system includes a start-up circuit, an indicator circuit, and a monitoring and control circuit. The start-up circuit includes an AC power supply, to which a water pump circuit and two or more electric heating circuits are connected in parallel. The water pump circuit includes a water pump circuit breaker, a motor starter, and a water pump connected in series; the electric heating circuit includes an electric heating circuit breaker, an AC contactor, and an electric heater connected in series. The indicating circuit and monitoring and control circuit are connected in parallel to the control power supply. The indicating circuit includes a pump indicating circuit, an electric heating operation circuit, and an electric heating fault indicating circuit, all connected in parallel to the control power supply. The pump indicating circuit is split into two parallel paths after passing through a bidirectional contact switch of the motor starter; one path carries a pump start indicator light, and the other carries a pump fault indicator light. The electric heating operation circuit is formed by connecting two or more normally open contact switches of electric heating relays in parallel and then connecting them in series with the electric heating operation indicator light. The electric heating fault indicating circuit is formed by connecting two or more normally closed contact switches of electric heating circuit breakers in parallel and then connecting them in series with the motor thermal fault indicator light. The monitoring and control circuit includes two or more electric heating temperature relays, a hot water thermostat, and a tank thermostat connected in parallel to the control power supply. All electric heating temperature relays, hot water thermostats, and tank thermostats are externally connected to temperature sensors. The sensor has a signal output terminal connected between the input terminal of the first electric heating temperature relay bidirectional contact switch and the motor starter bidirectional contact switch and the pump start indicator light. For two or more electric heating temperature relays, the other side of the output terminal of the preceding electric heating temperature relay bidirectional contact switch is connected to the input terminal of the following electric heating temperature relay bidirectional contact switch. The other side of the output terminal of the last electric heating temperature relay bidirectional contact switch is sequentially connected to the normally closed switch inside the tank thermostat, the normally closed switch inside the hot water thermostat, and the electric heating selector switch, then connected to the negative terminal of the control power supply in two or more stages. Each stage is equipped with a series-connected electric heating circuit breaker switch and an electric heating relay. One side of the output terminal of the bidirectional contact switch of two or more electric heating temperature relays is in contact with the signal output terminal, which is connected to the negative terminal of the control power supply via the over-temperature alarm indicator light.

[0007] It also includes a power-on indicator circuit on the parallel control power supply, and a power-on indicator light is provided on the power-on indicator circuit.

[0008] Each of the two or more electric heating temperature relays is connected to the positive terminal of the control power supply via a reset switch.

[0009] It also includes a phase sequence relay, a control power supply, and a selector switch. The water pump circuit is split into two paths after the water pump circuit breaker. One path is connected to the phase sequence relay, and the other path is connected to the control power supply. The control power supply is split into two paths via the selector switch. One path is connected to the motor starter, and the other path is connected to the control power supply. The motor starter is equipped with a two-way contact switch for the phase sequence relay.

[0010] The normally closed switch inside the hot water thermostat is connected to the first position switch of the electric heating selector switch. The first position switch of the electric heating selector switch is divided into multiple positions and connected in parallel to the negative terminal of the control power supply. The first position is connected in series with the electric heating circuit breaker switch and the electric heating relay. Each subsequent position is connected in series with the corresponding position switch of the electric heating selector switch, the electric heating circuit breaker switch, and the electric heating relay. Each subsequent position is connected in parallel with the electric heating circuit breaker switch and the electric heating relay of the previous position.

[0011] A counter is connected in parallel to the electric heating operation indicator light.

[0012] A counter is connected in parallel to the power-on indicator light.

[0013] The beneficial effects of this utility model are: 1. Reliable and controllable water pump operation: Through the cooperation of phase sequence relay and motor starter, the water pump phase sequence is automatically detected and the forward and reverse rotation is switched without manual intervention, avoiding operation failures caused by abnormal phase sequence and improving the water circulation heating efficiency.

[0014] 2. Comprehensive visualization of operating status: The system is equipped with power-on indicator, pump start indicator, fault indicator, electric heating operation indicator, and over-temperature alarm indicator. Combined with the running time counter, it enables comprehensive monitoring of power status, equipment operating status, fault information, and running time, allowing operators to keep track of the system status in real time.

[0015] 3. Precise and efficient temperature control: It adopts a triple temperature control mechanism of electric heating element temperature, outlet water temperature and tank medium temperature, which not only ensures the stability of the tank medium temperature, but also effectively protects the electric heating element from overheating damage; the multi-level heating switching design can adjust the heating load according to actual needs and reduce energy consumption.

[0016] 4. Timely and reliable fault protection: The electric heating circuit breaker and water pump circuit breaker realize short circuit and overload protection of the circuit, the over-temperature protection mechanism quickly cuts off the abnormal heating circuit, the fault indicator light accurately reflects the fault location, and the reset switch ensures that the system can be restarted after the fault is cleared, thus ensuring the safe operation of the system in all aspects. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of the starting circuit of this utility model; Figure 2 This is a circuit diagram of the indicator circuit of this utility model; Figure 3 This is the circuit diagram of the monitoring and control circuit of this utility model.

[0018] In the diagram: Operating AC power supply X0, operating selector switch Q1, selector switch Q2, first electric heating circuit breaker QF1, first electric heating circuit breaker normally closed switch QF1-1, first electric heating circuit breaker switch QF1-2, second electric heating circuit breaker QF2, second electric heating circuit breaker normally closed switch QF2-1, second electric heating circuit breaker switch QF2-2, third electric heating circuit breaker QF3, third electric heating circuit breaker normally closed switch QF3-1, third electric heating circuit breaker switch QF3-2, first AC contactor 1KM, second AC contactor 2KM, and so on. Three AC contactors 3KM, first electric heater EH1, second electric heater EH3, third electric heater EH4, water pump circuit breaker QF4, sequence relay K, sequence relay bidirectional contact switch K-1, motor starter K2, motor starter bidirectional contact switch K2-1, water pump M1, switching power supply TC1, control power supply positive L+, control power supply negative L-, power-on indicator H1, over-temperature alarm indicator H2, electric heater fault indicator H3, electric heater running indicator H4, pump start indicator H5, pump fault indicator H6, power-on time counter H7 Electric heating running time counter H8, signal input terminal PUMPON, signal output terminal OVERTEMP, electric heating selection switch (position 1) S1-1, electric heating selection switch (position 2) S1-2, electric heating selection switch (position 3) S1-3, reset switch S2, first electric heating temperature relay S3, first electric heating temperature relay bidirectional contact switch S3-1, second electric heating temperature relay S4, second electric heating temperature relay bidirectional contact switch S4-1, third electric heating temperature relay S5, third electric heating temperature relay bidirectional contact switch S4-1. 1. First temperature sensor B1, second temperature sensor B2, third temperature sensor B3, hot water thermostat TH1, hot water thermostat normally closed switch TH1-1, tank thermostat TH2, tank thermostat normally closed switch TH2-1, fourth temperature sensor B4, fifth temperature sensor B5, first electric heating relay KM1, first electric heating relay normally open contact KM1-1, second electric heating relay KM2, second electric heating relay normally open contact KM2-1, third electric heating relay KM3, third electric heating relay normally open contact KM3-1. Detailed Implementation

[0019] The following description, in conjunction with the accompanying drawings and embodiments, provides further details.

[0020] Figure 1-3As shown: A control circuit for a tank heating system includes an operation start-up circuit, an indicator circuit, and a monitoring and control circuit. The starting circuit includes an AC power supply X0. After passing through a selector switch Q1, a water pump circuit and three electric heating circuits are connected in parallel on the AC power supply X0. The water pump circuit includes a water pump circuit breaker QF4, a motor starter K2, and a water pump M1 connected in series. The first electric heating circuit includes a first electric heating circuit breaker QF1, an AC contactor 1KM, and a first electric heater EH1 connected in series. The second electric heating circuit includes a second electric heating circuit breaker QF2, an AC contactor 2KM, and a second electric heater EH2 connected in series. The third electric heating circuit includes a third electric heating circuit breaker QF3, an AC contactor 3KM, and an electric heater EH3 connected in series. The water pump circuit branches off into two paths after the water pump circuit breaker QF4. One path connects to a phase sequence relay K, and the other path connects to a control switch power supply TC1. The control switch power supply TC1 is further divided into two paths before the selector switch: one path connects to the motor starter control, and the other path connects to the control power supply. The motor starter K2 has a phase sequence relay bidirectional contact switch K-1.

[0021] The control power supply has parallel indicator circuits and monitoring and control circuits connected to its positive and negative terminals L+ and L+-. The indicator circuits include a power-on indicator circuit, a pump indicator circuit, an electric heating operation circuit, and an electric heating fault indicator circuit, all connected in parallel to the control power supply. The power-on indicator circuit has a power-on indicator light H1, with a power-on time counter H7 connected in parallel to it. The pump indicator circuit is divided into three parallel paths after passing through the motor starter bidirectional contact switch K2-1: the first path includes a pump start indicator light H5, the second path includes a pump fault indicator light H6, and the third path outputs a signal terminal PUMPON. The electric heating operation circuit consists of the first, second, and third electric heating relay normally open contact switches KM1-1, KM2-1, and KM3-1 connected in parallel, and then connected in series with the electric heating operation indicator light H4. A heating operation time counter H7 is connected in parallel to the heating operation indicator H4. The heating fault indication circuit is formed by connecting the normally closed contact switches QF1-1, QF2-1, and QF3-1 of the first, second, and third heating circuit breakers of the three heating circuits in parallel, and then connecting them in series with the motor heating fault indicator H3. The monitoring and control circuit includes the first, second, and third heating temperature relays S3, S4, and S5, the hot water thermostat TH1, and the tank thermostat TH2, all connected in parallel to the positive and negative terminals L+\+- of the control power supply. The first, second, and third heating temperature relays are externally connected to the first, second, and third temperature sensors B1, B2, and B3, which are used to monitor the heating of the electric heating. The hot water thermostat and the tank thermostat are externally connected to the fourth and fifth temperature sensors B4 and B5, which are used to monitor the temperature of the heated hot water and the temperature inside the storage tank. The first, second, and third electric heating temperature relays S3, S4, and S5 are connected to the control power supply, where a reset switch S2 is installed. The signal input terminal PUMPON is connected to the first electric heating temperature relay S3, which is then split into two paths via the first electric heating temperature relay bidirectional contact switch S3-1. One path connects to the signal output terminal OVERTEMP, and the other path connects to the second electric heating temperature relay S4, which is also split into two paths via the second electric heating temperature relay bidirectional contact switch S4-1. One path connects to the signal output terminal OVERTEMP, and the other path connects to the third electric heating temperature relay S5, which is also split into two paths via the third electric heating temperature relay bidirectional contact switch S5-1. One path connects to the signal output terminal OVERTEMP, and the other path connects sequentially to the normally closed switch TH2 inside the tank temperature controller. After the normally closed switch inside the water temperature controller TH1, the electric heating selector switch S1-1 is connected. After the electric heating selector switch S1-1, it is connected in sequence to the negative terminal L- of the control power supply via the first electric heating circuit breaker switch QF1-2 and the first electric heating relay KM1. The second electric heating circuit breaker switch QF1-2 and the first electric heating relay KM1 are connected in parallel to the second electric heating selector switch S1-2, the second electric heating circuit breaker switch QF2-2 and the second electric heating relay KM2, which are connected in series to the negative terminal L- of the control power supply. The third electric heating circuit breaker switch S3-2, the third electric heating circuit breaker switch QF3-2 and the third electric heating relay KM3 are connected in parallel to the second electric heating circuit breaker switch QF2-2 and the second electric heating relay KM2, which are connected in series to the third electric heating selector switch S3-2.The signal output terminal OVERTEMP is connected to the negative terminal of the control power supply via the over-temperature alarm indicator H2.

[0022] When the circuit in this embodiment is working: I. System Startup and Water Pump Operation Control: Closing the operation selection switches Q1 and Q2 connects the AC power supply X0, and the water pump circuit and electric heating circuit enter standby mode. The phase sequence relay K monitors the power phase sequence in real time. If the phase sequence is abnormal, its bidirectional contact switch K-1 automatically switches, controlling the motor starter K2 to adjust the running direction, ensuring that the water pump M1 always runs in the forward direction. The motor starter K2 also provides overload protection for the water pump. When the water pump load exceeds the rated value, it automatically cuts off the circuit to prevent equipment damage.

[0023] II. Visual Monitoring of Operating Status: After the control power is turned on, the power-on indicator H1 lights up, and the power-on time counter H7 starts synchronously, recording the overall system running time. When the water pump is running normally, the motor starter bidirectional contact switch K2-1 triggers the pump start indicator H5 to light up; if the water pump malfunctions, the contact switch switches to the fault circuit, the pump fault indicator H6 lights up, and the signal input terminal PUMPON feeds back a fault signal. When the electric heating is running, any AC contactor (1KM / 2KM / 3KM) is energized, the normally open contact of the corresponding electric heating relay (KM1-1 / KM2-1 / KM3-1) closes, the electric heating running indicator H4 lights up, and the electric heating running time counter H8 starts counting; if the electric heating circuit breaker (QF1 / QF2 / QF3) triggers protection to disconnect, its normally closed contact (QF1-1 / QF2-1 / QF3-1) closes, and the electric heating fault indicator H3 lights up.

[0024] III. Precise Temperature Control and Heating Level Adjustment: A triple temperature control mechanism works in tandem: The first, second, and third temperature sensors (B1 / B2 / B3) monitor the temperature of the electric heating element in real time and feed back to the corresponding temperature relays (S3 / S4 / S5); the fourth temperature sensor B4 detects the outlet water temperature and feeds back to the hot water thermostat TH1; the fifth temperature sensor B5 detects the temperature of the medium inside the tank and feeds back to the tank thermostat TH2. The electric heating level is switched via a selector switch (S1-1 / S1-2 / S1-3): Level 1 activates EH1, Level 2 is superimposed with EH2, and Level 3 is superimposed with EH3, achieving adjustment for different heating loads. Temperature control logic: When the temperature inside the tank or the outlet water temperature is lower than the set value, the normally closed switch (TH1-1 / TH2-1) of the temperature controller closes. If the temperature of the electric heating element is normal, the bidirectional contact switch (S3-1 / S4-1 / S5-1) of the temperature relay is turned on, and the corresponding electric heating relay is energized to start electric heating. When any temperature exceeds the set value, the corresponding switch is turned off and heating stops.

[0025] IV. Fault Protection and Reset Mechanism: Short Circuit and Overload Protection: The water pump circuit breaker QF4 and the electric heating circuit breakers (QF1 / QF2 / QF3) provide short circuit and overload protection for the water pump circuit and electric heating circuit respectively, immediately cutting off the main circuit in case of a fault. Over-Temperature Protection: When the temperature of the electric heating element exceeds the limit, the bidirectional contact switch of the temperature relay switches to the over-temperature circuit, triggering the over-temperature alarm indicator H2 at the signal output terminal OVERTEMP, and simultaneously cutting off the electric heating control circuit to prevent dry burning. Fault Reset: After the over-temperature fault is cleared, the reset switch S2 must be pressed to reset the temperature relay state before the electric heating system can be restarted to avoid repeated operation if the fault is not cleared.

Claims

1. A control circuit for a tank heating system, comprising a start-up circuit, an indicator circuit, and a monitoring and control circuit, characterized in that: The operation start-up circuit includes an AC power supply, to which a water pump circuit and an electric heating circuit are connected in parallel. The water pump circuit includes a water pump circuit breaker, a motor starter, and a water pump connected in series; the electric heating circuit includes an electric heating circuit breaker, an AC contactor, and an electric heater connected in series. The indicating circuit and monitoring control circuit are connected in parallel to the control power supply. The indicating circuit includes a pump indicating circuit, an electric heating operation circuit, and an electric heating fault indicating circuit, all connected in parallel to the control power supply. The pump indicating circuit is split into two parallel paths after passing through a bidirectional contact switch of the motor starter; one path carries a pump start indicator light, and the other carries a pump fault indicator light. The electric heating operation circuit is formed by connecting a normally open contact switch of an electric heating relay in parallel and then connecting it in series with the electric heating operation indicator light. The electric heating fault indicating circuit is formed by connecting a normally closed contact switch of an electric heating circuit breaker in parallel and then connecting it in series with the motor thermal fault indicator light. The monitoring control circuit includes an electric heating temperature relay connected in parallel to the control power supply. The hot water thermostat, the tank thermostat, the electric heating temperature relay, the hot water thermostat, and the tank thermostat are all externally connected to temperature sensors. The input terminal of the electric heating temperature relay's bidirectional contact switch is connected to the signal output terminal between the motor starter's bidirectional contact switch and the pump start indicator light. One side of the output terminal of the electric heating temperature relay's bidirectional contact switch is in contact with the signal output terminal, which is connected to the negative terminal of the control power supply via the over-temperature alarm indicator light. The other side of the output terminal of the electric heating temperature relay's bidirectional contact switch is connected sequentially to the normally closed switch inside the tank thermostat, the normally closed switch inside the hot water thermostat, the electric heating switch, the electric heating circuit breaker switch, and the electric heating relay connected to the negative terminal of the control power supply.

2. A control circuit for a tank heating system, comprising a start-up circuit, an indicator circuit, and a monitoring and control circuit, characterized in that: The operation start-up circuit includes an AC power supply, to which a water pump circuit and two or more electric heating circuits are connected in parallel. The water pump circuit includes a water pump circuit breaker, a motor starter, and a water pump connected in series; the electric heating circuit includes an electric heating circuit breaker, an AC contactor, and an electric heater connected in series. The indicating circuit and monitoring and control circuit are connected in parallel to the control power supply. The indicating circuit includes a pump indicating circuit, an electric heating operation circuit, and an electric heating fault indicating circuit, all connected in parallel to the control power supply. The pump indicating circuit is split into two parallel paths after passing through a bidirectional contact switch of the motor starter; one path carries a pump start indicator light, and the other carries a pump fault indicator light. The electric heating operation circuit is formed by connecting two or more normally open contact switches of electric heating relays in parallel and then connecting them in series with the electric heating operation indicator light. The electric heating fault indicating circuit is formed by connecting two or more normally closed contact switches of electric heating circuit breakers in parallel and then connecting them in series with the motor thermal fault indicator light. The monitoring and control circuit includes two or more electric heating temperature relays, a hot water thermostat, and a tank thermostat connected in parallel to the control power supply. All electric heating temperature relays, hot water thermostats, and tank thermostats are externally connected to temperature sensors. The sensor has a signal output terminal connected between the input terminal of the first electric heating temperature relay bidirectional contact switch and the motor starter bidirectional contact switch and the pump start indicator light. For two or more electric heating temperature relays, the other side of the output terminal of the preceding electric heating temperature relay bidirectional contact switch is connected to the input terminal of the following electric heating temperature relay bidirectional contact switch. The other side of the output terminal of the last electric heating temperature relay bidirectional contact switch is sequentially connected to the normally closed switch inside the tank thermostat, the normally closed switch inside the hot water thermostat, and the electric heating selector switch, then connected to the negative terminal of the control power supply in two or more stages. Each stage is equipped with a series-connected electric heating circuit breaker switch and an electric heating relay. One side of the output terminal of the bidirectional contact switch of two or more electric heating temperature relays is in contact with the signal output terminal, which is connected to the negative terminal of the control power supply via the over-temperature alarm indicator light.

3. A control circuit for a tank heating system according to claim 1 or 2, characterized in that: It also includes a power-on indicator circuit on the parallel control power supply, and a power-on indicator light is provided on the power-on indicator circuit.

4. A control circuit for a tank heating system according to claim 1 or 2, characterized in that: Each of the two or more electric heating temperature relays is connected to the positive terminal of the control power supply via a reset switch.

5. A tank heating system control circuit according to claim 1 or 2, characterised in that: It also includes a phase sequence relay, a control power supply, and a selector switch. The water pump circuit is split into two paths after the water pump circuit breaker. One path is connected to the phase sequence relay, and the other path is connected to the control power supply. The control power supply is split into two paths via the selector switch. One path is connected to the motor starter, and the other path is connected to the control power supply. The motor starter is equipped with a two-way contact switch for the phase sequence relay.

6. A tank heating system control circuit according to claim 2, wherein: The normally closed switch inside the hot water thermostat is connected to the first position switch of the electric heating selector switch. The first position switch of the electric heating selector switch is divided into multiple positions and connected in parallel to the negative terminal of the control power supply. The first position is connected in series with the electric heating circuit breaker switch and the electric heating relay. Each subsequent position is connected in series with the corresponding position switch of the electric heating selector switch, the electric heating circuit breaker switch, and the electric heating relay. Each subsequent position is connected in parallel with the electric heating circuit breaker switch and the electric heating relay of the previous position.

7. A control circuit for a tank heating system according to claim 1 or 2, characterized in that: A counter is connected in parallel to the electric heating operation indicator light.

8. The control circuit for a tank heating system according to claim 3, characterized in that: A counter is connected in parallel to the power-on indicator light.

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