The intermediate wire of the thermal resistor is broken
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There are two three-wire thermal resistors on site; it’s not clear who broke the middle wire. How can the 6 wires coming from the thermal resistors be matched with the 6 wires coming from the control system? The resistances measured for the three wires coming from the control unit are ab at 1.8k, ac at 1.8k, and bc at 1.5k. The resistances are ab103, ac103, and bc, all in the range of a few ohms. In this case, does it just require connecting the public terminal a, with the other terminals b and c being connected arbitrarily?
Since there are two temperature measurement points, first measure the resistance value – the resistance varies with temperature. First separate the 6 wires at the thermistor end, then conduct tests to check for short circuits; also separate the 6 wires at the control unit into 2 groups
First, short-circuit the three wires of one thermistor located on one side of the site, and open-circuit the three wires of the other thermistor. For those connected to the control unit, also short-circuit the three wires and open-circuit the other three. In this way, the corresponding set of wires between the thermistor and the control unit can be identified; the wire colors can then be used to make the connections. If the colors are the same, simply short-circuit the two wires and take a measurement....
There are two methods: one is to connect the wires based on their color, and the other is to short-circuit the wires together if they have the same color; using a multimeter to check for continuity will help identify the corresponding wires, and once they are connected, it’s done
Can you divide your 6 wires into groups of three each? It’s okay if the thermistor is short-circuited; just try it slowly.
First, short-circuit the three wires of one thermistor located on one side of the site, and open-circuit the three wires of the other thermistor; use a multimeter to check for continuity at each temperature measurement point. Then do the same for those connected to the DCS cabinet – short-circuit the three wires and open-circuit the other three, using a multimeter to check for continuity. In this way, the desired points can be identified.
For three-wire thermal resistors, the standard configuration is 2 red wires and 1 white wire; therefore, identifying these colors makes it much easier to find them. Find 2 red ones; if the resistance is approximately 0, they form a set. This set, along with another white one, is used to measure the resistance – a value of over 100 ohms indicates that it’s a lead of a thermistor. After finding one of the leads of a thermistor, the other set of 2 red and 1 white wires belongs to another thermistor. Next, it was connected to the central control system.
To accurately distinguish between the two sets of wiring, follow the steps below. 1. Disconnect one set of thermistor wires from the central control module, then short-circuit them in pairs to identify which set of thermistors it is. The remaining 3 wires are the wiring for another set of thermistors. The tag number should correspond to the measurement name. 2. Once the two sets of wires are clearly distinguished and the wiring is verified to be correct, the disconnected sections in between can be connected one by one in a corresponding manner, while ensuring proper insulation. 3. After verifying the resistance values of the two groups in the control room, the module can be connected. If the temperatures of the two groups are close, calibration can also be carried out by connecting a sensor to the connection point to measure the actual temperature, thereby ensuring absolute accuracy.