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This post was last edited by yunrun on 2021-7-27 22:24. Electric contact pressure gauges are widely used, for example in controlling the water pressure in pressure tanks； The operating pressure control of the vacuum pump, etc. Given the wide range of applications for electric contact pressure gauges, it is essential to master their wiring. In this article, Changhui Instruments shares with you typical applications of using electric contact pressure gauges to control the start and stop of motors, as well as the wiring methods for such pressure gauges. Wiring of electric contact pressure gauges: yunrun.com.cn/tech/3904.html. Working principle of electric contact pressure gauges: 1. An electric contact pressure gauge has three pointers – one is the pointer for indicating the actual pressure value (black), another is the pointer for indicating the lower pressure setting limit (green), and the last one is the pointer for indicating the upper pressure setting limit (red). 2. As for the specific working principle, Changhui Instruments explains it in terms of the pressure control in the pressure-boosting water tank: for example, when the pressure inside the tank (i.e., gauge pressure) is below 0.3 MP, the water supply motor starts to pump water ； When the pressure is above 0.6 MP, the water supply motor stops pumping. The control circuit of the water pump motor is shown in the following image: http://yunrun.com.cn/upload/202107/25/202107251903034067.png The main circuit is well-known to everyone, so no further explanation is needed; here we will focus on the control circuit. When the rotary selector switch is set to 1 and 5, it is in manual control mode, so no further explanation is needed here. When 1 and 8 are connected, it is under fully automatic control by an electric contact pressure gauge. In the fully automatic control mode of an electric contact pressure gauge, the actual pressure pointer is connected to the common line, namely line 1, which is also the power supply line. The lower limit pointer is connected to line 2. The upper limit pointer is connected to line 4. At the beginning, when the gauge pressure is zero, the actual pressure pointer is connected to the lower limit pointer; that is, 1 and 2 are connected, relay KA1 is activated, contactor KM1 is activated and self-locked, and the water pumping motor starts to operate. As the pump motor operates, the gauge pressure gradually increases; the actual pressure pointer moves away from the lower limit pointer and shifts toward higher pressure values. When the gauge pressure reaches the upper set value, the actual pressure pointer is connected to the upper limit pointer; that is, 1 and 4 are connected, relay KA2 is activated, contactor KM1 is disconnected, and the pumping motor stops operating. As the user continues to use water, the gauge pressure gradually decreases, and the actual pressure pointer moves downward until it makes contact with the lower limit pointer once again, at which point the next cycle of water supply begins. Wiring method for electric contact pressure gauges: The key to wiring an electric contact pressure gauge is to identify the common wire, the lower limit wire, and the upper limit wire. 1. Under normal circumstances, in a standard electric contact pressure gauge, the yellow wire is the common wire, that is, the power supply wire. The green line is the lower limit line, that is, the start line. The red line is the upper limit, that is, the stop line. The black line is the ground wire. 2. However, the author has encountered a electric contact pressure gauge that does not conform to the standards; after connecting the wires according to the aforementioned color codes and switching it to automatic mode, attempting to start it up by applying power resulted in the motor not working. In such a situation, the following method is needed: ① There are 4 wires inside the wiring box of the electric contact pressure gauge; the wire connected to the metal casing is the ground wire, which is easy to find. ②For the remaining 3 wires, use a multimeter in continuity mode to identify the 2 wires that are connected to each other. Connect the power line (i.e., the common line) and the start line to these two wires, without worrying for now whether they are connected in reverse or not. ③The last remaining wire determines which one will be connected to the stop wire. ④Set the switch to automatic, turn on the power to test it, and let the water pump draw water. At this point, pay attention to the gauge pressure; if it reaches the maximum pressure and the water pump stops, it indicates that the wiring is correct. ⑤If the pressure reaches the maximum level and the water pump keeps running, it means that the positions of the power cable (i.e., the common wire) and the start wire are reversed. Swap the two positions and reconnect the wires. 3. The third method is to directly examine the wiring of the watch hand mechanism. Facing the front of the electric contact pressure gauge, from outside to inside, they are as follows: the first wire is the ground wire, the second wire is the power supply wire (i.e., the common wire), the third wire is the start wire, and the fourth is the stop wire. Troubleshooting common issues with electric contact pressure gauges: Due to the frequent swinging of the pointer in such gauges, the pointer makes repeated contacts and disconnections, which can cause arcing at the contact points. Over time, this leads to poor connections and prevents the circuit from conducting electricity. Therefore, in the control circuit of electric contact pressure gauges, contactors with high coil power should not be used; instead, relay relays with low power should be employed. This is how the service life of electric contact pressure gauges can be extended. This concludes the discussion on typical applications of electric contact pressure gauges for controlling the start and stop of motors, as well as the wiring procedures for such gauges. Please feel free to point out any shortcomings. Thank you! Author: Wen Jie