Three-phase relay detection circuit

Abstract

The invention relates to a three-phase relay detection circuit, which comprises a leakage protector, a voltage regulator, a fuse, a power supply regulation module, a power supply regulation control module and a first relay, and is characterized in that the leakage protector is connected with three-phase power, the output end of the leakage protector is connected with the voltage regulator, and the output end of the voltage regulator is connected with one end of the fuse; the other end of the fuse is connected with the input end of the power supply adjusting module, the power supply adjusting module is connected with the power supply adjusting control module, the output of the power supply adjusting module is connected with the first relay, and the output of the first relay is connected with the tested relay. Compared with the prior art, the method has the advantages of improving the accuracy of circuit detection and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of three-phase relay detection, and particularly to a three-phase relay detection circuit. Background Art

[0002] The detection of three-phase relays requires high-voltage operation. Currently, when wiring for the detection of three-phase relays, it is necessary to manually adjust the forward voltage, reverse voltage, and the missing phase wire, which is time-consuming and laborious. High-voltage operation is also prone to the risk of electric shock, and the safety of the three-phase relay detection circuit is insufficient.

[0003] In addition, when testing the operation of three-phase relays under different conditions of forward voltage, reverse voltage, and missing phase, if an operation error occurs and the voltages of the two situations are applied to the relay under test simultaneously, it will affect the test results, resulting in inaccurate test results, and thus it is impossible to determine whether the relay under test is damaged. Summary of the Invention

[0004] An object of the present invention is to provide a three-phase relay detection circuit for improving safety and the accuracy of relay detection.

[0005] The object of the present invention can be achieved by the following technical solutions:

[0006] A three-phase relay detection circuit, the circuit includes a leakage protector, a voltage regulator, a fuse, a power supply adjustment module, a power supply adjustment control module, and a first relay. Among them, the leakage protector is connected to three-phase electricity, the output end of the leakage protector is connected to the voltage regulator, the output end of the voltage regulator is connected to one end of the fuse, the other end of the fuse is connected to the input end of the power supply adjustment module, the power supply adjustment module is connected to the power supply adjustment control module, the output of the power supply adjustment module is connected to the first relay, and the output of the first relay is connected to the relay under test.

[0007] Further, the leakage protector Q1 is connected to three-phase electricity W1, V1, and U1, the output ends of the leakage protector are respectively the three-phase electricity W, V, and U ends, the output ends of the leakage protector are respectively connected to the normally open ends of the contactor K1, the common end of the contactor K1 is the three-phase electricity A, B, and C ends, and the coil of the contactor K1 is connected to the W end among the output ends of the leakage protector.

[0008] Further, the three-phase electricity A, B, and C ends are connected to the input end of the voltage regulator, the output end of the voltage regulator is connected to one end of the fuse, and the other end of the fuse is respectively connected to the three-phase electricity U, V, and W ends.

[0009] Furthermore, the power supply regulation module includes a forward power supply module, a V-phase missing power supply module, a W-phase missing power supply module, and a reverse power supply module. The forward power supply module includes the contacts of relays K2 and K3. The V-phase missing power supply module includes the contacts of relays K4 and K5. The W-phase missing power supply module includes the contact of relay K6. The reverse power supply module includes the contacts of relays K8 and K9.

[0010] Furthermore, the first normally open end of relay K2 is connected to the U terminal of the three-phase power supply. The second normally open end of relay K2 is connected to the V terminal of the three-phase power supply. The first common end of relay K2 is connected to the U2 terminal of the three-phase power supply. The second common end of relay K2 is connected to the V2 terminal of the three-phase power supply.

[0011] The first normally open end of relay K3 is connected to the W terminal of the three-phase power supply. The first common end of relay K3 is connected to the W2 terminal of the three-phase power supply.

[0012] The first normally open end of relay K4 is connected to the U terminal of the three-phase power supply. The first common end of relay K4 is connected to the U2 terminal of the three-phase power supply.

[0013] The first normally open end of relay K5 is connected to the W terminal of the three-phase power supply. The first common end of relay K5 is connected to the W2 terminal of the three-phase power supply.

[0014] The first normally open end of relay K6 is connected to the U terminal of the three-phase power supply. The second normally open end of relay K6 is connected to the V terminal of the three-phase power supply. The first common end of relay K6 is connected to the U2 terminal of the three-phase power supply. The second common end of relay K6 is connected to the V2 terminal of the three-phase power supply.

[0015] The first normally open end of relay K8 is connected to the U terminal of the three-phase power supply. The second normally open end of relay K2 is connected to the V terminal of the three-phase power supply. The first common end of relay K2 is connected to the W2 terminal of the three-phase power supply. The second common end of relay K2 is connected to the V2 terminal of the three-phase power supply.

[0016] The first normally open end of relay K9 is connected to the W terminal of the three-phase power supply. The first common end of relay K9 is connected to the U2 terminal of the three-phase power supply.

[0017] Furthermore, the U2, V2, and W2 terminals of the three-phase power supply are respectively connected to the L1, L2, and L3 terminals of the three-phase power supply. The L1, L2, and L3 terminals are connected to the normally open ends of the forward power supply terminal, the V-phase missing terminal, the W-phase missing terminal, and the reverse power supply terminal of the first relay.

[0018] Furthermore, the power supply regulation control module includes the contacts of relays K10, K11, K12, and K13, and also includes the coils of relays K3, K2, K4, K5, K6, K7, K8, and K9.

[0019] Further, the coils of relay K3 and relay K2 are connected in parallel to form a first parallel unit. One end of the first parallel unit is connected to the normally open end of relay K10, and the normally closed end of relay K10 is connected to the positive voltage.

[0020] The coils of relay K4 and relay K5 are connected in parallel to form a second parallel unit. One end of the second parallel unit is connected to the normally open end of relay K11, and the normally closed end of relay K11 is connected to the positive voltage.

[0021] The coils of relay K6 and relay K7 are connected in parallel to form a third parallel unit. One end of the third parallel unit is connected to the normally open end of relay K12, and the normally closed end of relay K12 is connected to the positive voltage.

[0022] The coils of relay K8 and relay K9 are connected in parallel to form a fourth parallel unit. One end of the fourth parallel unit is connected to the normally open end of relay K13, and the normally closed end of relay K13 is connected to the positive voltage.

[0023] Further, the other end of the first parallel unit is connected to the second normally closed end of relay K9, and the second common end of relay K9 is grounded.

[0024] The other end of the second parallel unit is connected to the second normally closed end of relay K7, and the second common end of relay K7 is grounded.

[0025] The other end of the third parallel unit is connected to the second normally closed end of relay K4, and the second common end of relay K4 is grounded.

[0026] The other end of the fourth parallel unit is connected to the second normally closed end of relay K3. The second common end of relay K3 is connected to the second normally closed end of relay K5. The second common end of relay K5 is connected to the second normally closed end of relay K7. The second common end of relay K7 is grounded.

[0027] Further, the common end of the first relay is connected to the relay under test.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention protects the circuit by setting a leakage protector and a fuse, controls the on-off of the power supply adjustment control module during the operation of the circuit, selects the voltages of different situations that need to be led out. After leading out, it is determined by the first relay whether to lead the voltage of this situation to the relay under test, rather than immediately leading the voltage of this situation to the relay under test as soon as it is connected, which improves the overall safety. Moreover, the voltages of the four situations are interlocked in the power supply adjustment control module, and only one situation of voltage can be led out each time, which improves the accuracy of detection. Description of the Drawings

[0030] Figure 1The circuit structure diagram of the present invention;

[0031] Figure 2 The circuit diagram of the leakage protector and the contactor K1 of the present invention;

[0032] Figure 3 The circuit diagram of the voltage regulator and the fuse of the present invention;

[0033] Figure 4 The circuit diagram of the power supply regulation module of the present invention;

[0034] Figure 5 The circuit of the power supply regulation control module of the present invention. Specific embodiments

[0035] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0036] It should be noted that: similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0037] Some embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0038] The present invention provides a three-phase relay detection circuit. The overall structure diagram of the three-phase relay detection circuit is as Figure 1 shown. The circuit includes a leakage protector, a voltage regulator, a fuse, a power supply regulation module, a power supply regulation control module and a first relay. Among them, the leakage protector is connected to three-phase electricity, the output end of the leakage protector is connected to the voltage regulator, the output end of the voltage regulator is connected to one end of the fuse, the other end of the fuse is connected to the input end of the power supply regulation module, the power supply regulation module is connected to the power supply regulation control module, the output of the power supply regulation module is connected to the first relay, and the output of the first relay is connected to the relay to be measured.

[0039] The model of the leakage protector of the present invention is NVBLE-63. The leakage protector Q1 is connected to three-phase power W1, V1, and U1. The output terminals of the leakage protector are the three-phase power W, V, and U terminals respectively. The output terminals of the leakage protector are respectively connected to the normally open terminals of the contactor K1. The common terminal of the contactor K1 is the three-phase power A, B, and C terminals. The coil of the contactor K1 is connected to the W terminal among the output terminals of the leakage protector. The three-phase power W1, V1, and U1 are three-phase voltages provided by an AC power supply. When there is electricity at the W terminal, the coil of the contactor K1 conducts. There is conduction between the normally closed terminal and the common terminal of the contactor K1. The three-phase power is output from the three-phase power W, V, and U terminals, and then passes through the contacts of the contactor K1 and enters the three-phase power A, B, and C terminals. The circuit diagrams of the leakage protector and the contactor K1 are as shown in Figure 2 shown.

[0040] The three-phase power A, B, and C terminals of the present invention are connected to the input terminal of a voltage regulator. The output terminal of the voltage regulator is connected to one end of a fuse. The other end of the fuse is respectively connected to the three-phase power U, V, and W terminals. The voltage regulator of the present invention can be a TSGC2 three-phase voltage regulator. The circuit diagrams of the voltage regulator and the fuse are as shown in Figure 3 shown. The three-phase voltage regulator can control the turntable of the voltage regulator through the output terminal of a motor to achieve voltage regulation.

[0041] The three ports of the output terminal of the voltage regulator are respectively connected to fuses F4, F5, and F6. The fuses F4, F5, and F6 can be used to protect the circuit and prevent damage to devices due to excessive voltage.

[0042] The three-phase power A, B, and C terminals can also be connected to a rectifier. The rectifier rectifies the alternating current and outputs a direct current of 24V. The direct current can be input to a first relay for power supply.

[0043] The circuit diagram of the power supply regulation module is as shown in Figure 4 shown. The power supply regulation module includes a forward power supply module, a V-phase missing power supply module, a W-phase missing power supply module, and a reverse power supply module. The forward power supply module includes the contacts of relays K2 and K3. The V-phase missing power supply module includes the contacts of relays K4 and K5. The W-phase missing power supply module includes the contact of relay K6. The reverse power supply module includes the contacts of relays K8 and K9.

[0044] The first normally open terminal of relay K2 is connected to the three-phase power U terminal. The second normally open terminal of relay K2 is connected to the three-phase power V terminal. The first common terminal of relay K2 is connected to the three-phase power U2 terminal. The second common terminal of relay K2 is connected to the three-phase power V2 terminal;

[0045] The first normally open terminal of relay K3 is connected to the three-phase power W terminal; The first common terminal of relay K3 is connected to the three-phase power W2 terminal;

[0046] The first normally open terminal of relay K4 is connected to the three-phase power U terminal. The first common terminal of relay K4 is connected to the three-phase power U2 terminal;

[0047] The first normally open terminal of relay K5 is connected to the W terminal of the three-phase power supply, and the first common terminal of relay K5 is connected to the W2 terminal of the three-phase power supply;

[0048] The first normally open terminal of relay K6 is connected to the U terminal of the three-phase power supply, the second normally open terminal of relay K6 is connected to the V terminal of the three-phase power supply, the first common terminal of relay K6 is connected to the U2 terminal of the three-phase power supply, and the second common terminal of relay K6 is connected to the V2 terminal of the three-phase power supply;

[0049] The first normally open terminal of relay K8 is connected to the U terminal of the three-phase power supply, the second normally open terminal of relay K2 is connected to the V terminal of the three-phase power supply, the first common terminal of relay K2 is connected to the W2 terminal of the three-phase power supply, and the second common terminal of relay K2 is connected to the V2 terminal of the three-phase power supply;

[0050] The first normally open terminal of relay K9 is connected to the W terminal of the three-phase power supply, and the first common terminal of relay K9 is connected to the U2 terminal of the three-phase power supply.

[0051] The power supply regulation module is used to extract the three-phase voltages in four cases: positive power supply, V-phase missing power supply, W-phase missing power supply, and reverse power supply. The extracted voltages are connected to the U2, V2, and W2 terminals of the three-phase power supply.

[0052] The U2, V2, and W2 terminals of the three-phase power supply are respectively connected to the L1, L2, and L3 terminals of the three-phase power supply. The L1, L2, and L3 terminals are connected to the normally open terminals of the positive power supply terminal, V-phase missing terminal, W-phase missing terminal, and reverse power supply terminal of the first relay.

[0053] When one channel of the first relay is turned on, the L1, L2, and L3 terminals are turned on with a common terminal of the first relay. The common terminal of the first relay is connected to the relay under test. The first relay is provided with a positive power supply terminal, a V-phase missing terminal, a W-phase missing terminal, and a reverse power supply terminal. Each of the four terminals is provided with a common terminal, a normally open terminal, and a normally closed terminal. The L1, L2, and L3 terminals are all connected to the normally open terminals of the four terminals.

[0054] The power supply regulation control module is used to control the on-off of the contacts of the power supply regulation module. The circuit of the power supply regulation control module is as Figure 5 shown. The power supply regulation control module includes the contacts of relays K10, K11, K12, and K13, and also includes the coils of relays K3, K2, K4, K5, K6, K7, K8, and K9.

[0055] The coils of relay K3 and relay K2 are connected in parallel to form a first parallel unit. One end of the first parallel unit is connected to the normally open terminal of relay K10, and the normally closed terminal of relay K10 is connected to the positive voltage;

[0056] The coils of relay K4 and relay K5 are connected in parallel to form a second parallel unit. One end of the second parallel unit is connected to the normally open end of relay K11, and the normally closed end of relay K11 is connected to the positive voltage.

[0057] The coils of relay K6 and relay K7 are connected in parallel to form a third parallel unit. One end of the third parallel unit is connected to the normally open end of relay K12, and the normally closed end of relay K12 is connected to the positive voltage.

[0058] The coils of relay K8 and relay K9 are connected in parallel to form a fourth parallel unit. One end of the fourth parallel unit is connected to the normally open end of relay K13, and the normally closed end of relay K13 is connected to the positive voltage.

[0059] The coils of relays K10, K11, K12, and K13 can be connected to the output of the controller.

[0060] The other end of the first parallel unit is connected to the second normally closed end of relay K9, and the second common end of relay K9 is grounded.

[0061] The other end of the second parallel unit is connected to the second normally closed end of relay K7, and the second common end of relay K7 is grounded.

[0062] The other end of the third parallel unit is connected to the second normally closed end of relay K4, and the second common end of relay K4 is grounded.

[0063] The other end of the fourth parallel unit is connected to the second normally closed end of relay K3. The second common end of relay K3 is connected to the second normally closed end of relay K5. The second common end of relay K5 is connected to the second normally closed end of relay K7. The second common end of relay K7 is grounded.

[0064] The working principle of the power supply regulation control module and power supply regulation is as follows:

[0065] First, based on the output of the controller, any one of the coils of relays K10, K11, K12, and K13 is controlled to conduct. The parallel unit corresponding to the conducting coil is connected to the voltage, so the common end and the normally open end corresponding to the contact of this parallel unit conduct, and then the corresponding power supply module conducts, leading the voltage to the first relay.

[0066] Taking the relay K10 as an example, when the relay K10 is turned on, the coils of the relays K2 and K3 are both turned on at this time. The first common terminal and the first normally open terminal of the relay K2 of the positive power supply module are turned on, and the second common terminal and the second normally open terminal of the relay K2 are turned on. At the same time, the first common terminal and the first normally open terminal of the relay K3 of the positive power supply module are turned on. The VWM three-phase positive voltage is led to U2, W2, and V2, and then connected to L1, L2, and L3, and connected to the normally open terminal of the positive power supply terminal of the first relay. Control the coil of the positive power supply terminal of the first relay to be energized. The common terminal and the normally open terminal of the positive power supply terminal of the first relay are turned on. The positive voltage is output from the common terminal of the positive power supply terminal and applied to the relay under test, and then the test of the relay is carried out.

[0067] Similarly, when the relay K11 is turned on, the coils of K4 and K5 are turned on. The voltage lacking the V phase is led to U2, W2, and V2, and then connected to L1, L2, and L3, and connected to the normally open terminal of the terminal lacking the V phase of the first relay. At this time, control the coil of the terminal lacking the V phase of the first relay to be energized. The voltage lacking the V phase enters the common terminal lacking the V phase from the normally open terminal, and the voltage lacking the V phase is output from the common terminal lacking the V phase and applied to the relay under test, and then the test of the relay is carried out.

[0068] The same applies to the relays K12 and K13.

[0069] Taking the relay K10 as an example, when the relay K10 is turned on and the coils of the relays K2 and K3 are both turned on, the second common terminal and the second normally open terminal of the relay K3 are turned on. At this time, the fourth parallel unit is disconnected. Therefore, the power supply adjustment control module also plays a role of interlocking. When any power supply module is turned on, the other power supply modules are turned off.

[0070] Similarly, when the relay K11 is turned on, the second common terminal and the second normally open terminal of the relays K4 and K5 are turned on. At this time, the third parallel unit and the fourth parallel unit are disconnected to achieve interlocking.

[0071] In the present invention, the model of the relay under test for three-phase is RM22TR33. The voltage output by the first relay can be applied to the normally open terminal / normally closed terminal of the relay under test, and then the voltages and resistances of the normally closed 11 / 12, 21 / 22, and the normally open 11 / 14, 21 / 24 terminals of the relay under test are measured to determine whether the state of the relay under test is damaged.

[0072] In the present invention, the first relay is a 4-channel YF-24 relay. The contactor K1 is a 1210 contactor.

[0073] The adoption of the above device enables us to connect the test platform to the three-phase relay during the maintenance process, avoiding the potential safety hazards and the risk of relay burnout caused by directly manually connecting to 380V. It saves the wiring time and eliminates the need to measure the resistance value with a multimeter. The value can be directly displayed on the test panel. Through the conversion of the three-phase voltage regulator and the intermediate relay, the test can be directly achieved by operating the buttons on the panel, saving a lot of time and ensuring safety at the same time.

[0074] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in this technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art shall fall within the protection scope determined by the claims.

Claims

1. A three-phase relay detection circuit, characterized in that, The circuit includes a leakage protector, a voltage regulator, a fuse, a power supply regulation module, a power supply regulation control module, and a first relay. Among them, the leakage protector is connected to three-phase power, the output end of the leakage protector is connected to the voltage regulator, the output end of the voltage regulator is connected to one end of the fuse, the other end of the fuse is connected to the input end of the power supply regulation module, the power supply regulation module is connected to the power supply regulation control module, the output of the power supply regulation module is connected to the first relay, and the output of the first relay is connected to the relay under test.

2. The three-phase relay detection circuit according to claim 1, wherein The leakage protector Q1 is connected to three-phase power W1, V1, and U1. The output ends of the leakage protector are the three-phase power W, V, and U terminals respectively. The output ends of the leakage protector are respectively connected to the normally open terminals of the contactor K1. The common terminal of the contactor K1 is the three-phase power A, B, and C terminals. The coil of the contactor K1 is connected to the W terminal among the output ends of the leakage protector.

3. The three-phase relay detection circuit according to claim 2, characterized in that, The three-phase power A, B, and C terminals are connected to the input end of the voltage regulator. The output end of the voltage regulator is connected to one end of the fuse. The other end of the fuse is respectively connected to the three-phase power U, V, and W terminals.

4. A three-phase relay detection circuit according to claim 3, characterized in that, The power supply regulation module includes a forward power supply module, a V-phase missing power supply module, a W-phase missing power supply module, and a reverse power supply module. The forward power supply module includes the contacts of relays K2 and K3. The V-phase missing power supply module includes the contacts of relays K4 and K5. The W-phase missing power supply module includes the contact of relay K6. The reverse power supply module includes the contacts of relays K8 and K9.

5. The three-phase relay detection circuit according to claim 4, characterized in that, The first normally open terminal of relay K2 is connected to the three-phase power U terminal. The second normally open terminal of relay K2 is connected to the three-phase power V terminal. The first common terminal of relay K2 is connected to the three-phase power U2 terminal. The second common terminal of relay K2 is connected to the three-phase power V2 terminal. The first normally open terminal of relay K3 is connected to the three-phase power W terminal. The first common terminal of relay K3 is connected to the three-phase power W2 terminal. The first normally open terminal of relay K4 is connected to the three-phase power U terminal. The first common terminal of relay K4 is connected to the three-phase power U2 terminal. The first normally open terminal of relay K5 is connected to the three-phase power W terminal. The first common terminal of relay K5 is connected to the three-phase power W2 terminal. The first normally open terminal of relay K6 is connected to the three-phase power U terminal. The second normally open terminal of relay K6 is connected to the three-phase power V terminal. The first common terminal of relay K6 is connected to the three-phase power U2 terminal. The second common terminal of relay K6 is connected to the three-phase power V2 terminal. The first normally open terminal of relay K8 is connected to the three-phase power U terminal. The second normally open terminal of relay K2 is connected to the three-phase power V terminal. The first common terminal of relay K2 is connected to the three-phase power W2 terminal. The second common terminal of relay K2 is connected to the three-phase power V2 terminal. The first normally open terminal of relay K9 is connected to the three-phase power W terminal. The first common terminal of relay K9 is connected to the three-phase power U2 terminal.

6. The three-phase relay detection circuit according to claim 5, wherein, The three-phase power U2, V2, and W2 terminals are respectively connected to the three-phase power L1, L2, and L3 terminals. The L1, L2, and L3 terminals are connected to the normally open terminals of the forward power supply terminal, V-phase missing terminal, W-phase missing terminal, and reverse power supply terminal of the first relay.

7. The three-phase relay detection circuit according to claim 6, characterized in that, The power supply adjustment control module includes the contacts of relays K10, K11, K12, and K13, and also includes the coils of relays K3, K2, K4, K5, K6, K7, K8, and K9.

8. A three-phase relay detection circuit according to claim 7, characterized in that, The coil of relay K3 and the coil of relay K2 are connected in parallel to form a first parallel unit. One end of the first parallel unit is connected to the normally open end of relay K10, and the normally closed end of relay K10 is connected to the positive voltage. The coil of relay K4 and the coil of relay K5 are connected in parallel to form a second parallel unit. One end of the second parallel unit is connected to the normally open end of relay K11, and the normally closed end of relay K11 is connected to the positive voltage. The coil of relay K6 and the coil of relay K7 are connected in parallel to form a third parallel unit. One end of the third parallel unit is connected to the normally open end of relay K12, and the normally closed end of relay K12 is connected to the positive voltage. The coil of relay K8 and the coil of relay K9 are connected in parallel to form a fourth parallel unit. One end of the fourth parallel unit is connected to the normally open end of relay K13, and the normally closed end of relay K13 is connected to the positive voltage.

9. The three-phase relay detection circuit according to claim 8, wherein, The other end of the first parallel unit is connected to the second normally closed end of relay K9, and the second common end of relay K9 is grounded. The other end of the second parallel unit is connected to the second normally closed end of relay K7, and the second common end of relay K7 is grounded. The other end of the third parallel unit is connected to the second normally closed end of relay K4, and the second common end of relay K4 is grounded. The other end of the fourth parallel unit is connected to the second normally closed end of relay K3. The second common end of relay K3 is connected to the second normally closed end of relay K5. The second common end of relay K5 is connected to the second normally closed end of relay K7. The second common end of relay K7 is grounded.

10. A three-phase relay detection circuit according to claim 1, characterized in that, The common end of the first relay is connected to the relay under test.

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