I ran into a strange problem today: the control valves on the DCS show normal readings, but the display on the positioners isn’t lit, and the control valves won’t move
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To be more specific, after disconnecting the ± terminals after trading hours, the measured voltage was 24 volts. The positive terminal has no connection to ground, the negative terminal also has no connection to ground; the wires used for calibration are from this same set. The measured current is 50% of 12 mA, which matches the expected values. However, when the ± terminals are connected together, without a safety barrier in place, the measured voltage is only 0.9 V. The other AO points, when connected to control valve loads, show a normal voltage of 10 V. It is the low voltage of 0.9 V that prevents the actuator from functioning. I forgot to ask whether the voltage was measured with the wires disconnected at the site! ! ! ! What is the reason? ? ?
Is the locator broken? How about trying a different locator?
It’s most likely a fault with the locator, along with an excessively high load resistance, which causes a significant voltage drop
Measure the voltage at the site; there might be a problem with the wiring there. Generally, if the voltage at the site is below 12V, the smart locator will not operate stably
There must be some poor contacts in the cable; measure the resistance of the wire
Here, it works properly when the voltage is reduced to 10V
How long is the line? Is it over 500 meters?
Check whether the cable is damaged, or try using another cable of the same type or a safety barrier to see if the load is insufficient