How to convert active analog signals into passive signals
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The factory has been upgraded with a new radar gauge; it is a four-wire type that operates on 24VDC power, and it outputs a signal of 4-20mA along with 24V voltage. The DCS system used is from ABB. Previously, the channel modules used were of the AI801 type, and those channels were active channels (with 24VDC voltage measurable at the terminals). Now, how can this signal be integrated into the system? Isolators do not have this functionality. I am currently looking for a way to convert active signals into passive signals, so that the DCS can receive them as two-wire instruments. The problem now is that we can’t operate the DCS, as no one understands it. Does anyone have a solution? Wait at the scene for the festival.
The 4-20mA signal can be directly fed into the isolator; no 24V voltage is required.
What isolator? Check the DCS hardware manual; it usually shows the wiring method for passive points
Today, a passive isolator was used in the circuit: the 4-20MA (live) signal wire from the instrument was connected to the input terminal of the isolator; a voltage of 10V was detected at the output terminal. Then, the signal wire coming from the DCS terminal (with 24VDC) was connected as well, and a multimeter was used to measure the current, but no current was detected.
The problem now is that the DCS won’t work, which is causing headaches; I’m not familiar with the ABB AI801 module. In any case, it’s a two-wire circuit that is powered.
Non-selectable active current output for radar configuration?
Is there any isolator that has this function: it accepts an active analog input and outputs a passive analog signal, allowing the output to be used as a two-wire transmitter so that the DCS card can retrieve a 4-20mA signal?
Do not connect to the DCS yet; use a multimeter to measure the current signal at the input terminal. If there is a current signal at the input, then use the multimeter to check whether there is a current signal at the output terminal. If no current signal is detected there, it indicates that the isolator is faulty.
The function of the isolation module is to isolate the field signals from the control room; an input of 4-20mA should result in an output of 4-20mA as well.
After connecting to the DCS, it was found that there was no change in signal from the upper-level computer; the instrument was receiving proper power supply, and the 485 connection to the computer was working fine. The software displayed the actual material level as 20 meters, and the output current value as 16 mA. I carried out the following actions: 1. Disconnected the two wires connected to the isolator and used a multimeter to measure the 4-20 mA output of the instrument; the result was 16 mA, with a voltage of 20 VDC. 2. Connected the instrument to the input side of the isolator, disconnected the wire at the output side, and measured the output; the value again was 16 mA； The voltage measured was 10VDC. The DCS cable was connected; current was measured in series (the positive terminal of the DCS cable was connected to the output terminal, while its negative terminal was connected to the negative lead of the multimeter; the positive lead of the multimeter was connected to the negative terminal of the isolator). The measured current value was 0