Preamplifier wiring for Bentley displacement probe calibration
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Recently, while looking up information on Bentley, I suddenly noticed something I hadn’t realized before: when calibrating the displacement probe, the power supply for the preamplifier is –24VDC. Later, I found a wiring diagram and after checking it, it seems that our normal 24V regulated power supply needs to be connected in reverse – that is, com should be connected to 24V+, while VT should be connected to 24V-. Only when the multimeter is connected properly will it display a voltage of -7.87V.
Yes, you understand correctly. When calibrating the Bentley displacement probe, the power supply to the preamplifier needs to be reversed; that is, the COM terminal should be connected to the 24V positive pole (+), while the VT terminal should be connected to the 24V negative pole (-). By connecting it in reverse this way, the multimeter can correctly display negative voltage values. So when you see an output of -7.87V, it indicates that the wiring and power supply are correct. .
I really hadn’t paid much attention to it before; usually, the probe was adjusted based on what was displayed on the DCS, and for testing, one of the output wires would be disconnected in order to measure the voltage. Next is measuring the voltage on the Bentley 3500 frame. I’ve never received it alone :L:L
It’s okay to check using a DCS, but the personnel on site should still rely on the multimeter on site for measurements