Convert 4-wire transmitter to 2-wire operation

1. Transfer the 4-20 milliampere output from the original two-wire system to the four-wire instrument to the DCS system. 2. Look for electrical panels or power supply boxes near the instrument; a transformer can be used to convert the voltage to 24V in order to provide power locally, which helps to save on cables. 3. The input wiring for the DCS system, which was previously powered by the system itself or by a safety barrier, should now be powered externally, with it only accepting 4-20 milliampere signals.

Dude, did you solve your problem? I’ve run into this problem too. Could you please advise on how to solve this?

The last edit to this post was made by Xin Chang Xiao Xu on 2024-10-3 at 17:23. First, it’s necessary to check whether your instrument has the capability for two-wire transmission of signals; there are options available on the terminal blocks that allow selection between passive signal output and active signal output. Here, the terms \"passive\" and \"active\" refer to the instrument itself. Passive signal output means that the power supply is provided by the DCS, and the instrument functions like a resistor, with the current level being adjusted according to the set values. For active signal output, DCS does not supply power; the instrument obtains its own power source and generates a 4-20MA current based on the engineering value. If your instrument has only two terminals other than those for the power supply, used as signal outputs, then it can only provide passive signal outputs. Secondly, instruments with independent power supply have high power levels, making it impossible to use a two-wire system. The current required for power supply by a DCS is at least 4 mA; if the current needed for the instrument to function properly is greater than 4 mA, then a two-wire system cannot be used. You can create a small explosion-proof box; there are surely other instruments at the site that have their own power supply. By feeding 24V DC power into this box and using wiring to derive N pairs of power outputs, you can connect them to your existing instruments to supply them with power. What I do now is use an explosion-proof box with dimensions of 400*500*200. There are 3 1-inch connectors on the left side, 1 ¼-inch connector, two rows of 16 ¼-inch connectors on the upper side, and two rows of 16 connectors on the lower side. The box contains 64 terminal blocks, as well as ten terminal blocks each for the positive and negative 24V power supplies, with fuses installed on the positive terminals. Use a 24-core cable to connect the DCS side to the explosion-proof box; 3 of these cores can be used for 32 analog input/output signals or digital input/output signals. When used for modular input signals, 32 analog input signals can be provided. There is also a 4-way port on the left side, which serves as an inlet for 24V DC power. A 2-core power cable with a cross-sectional area of 1.5 square millimeters can be used, and after being connected to the box, it is divided into 10 individual power cables. For instruments that require separate power supply, a 4-core cable should be used – first connect the signal cables and then the power cables. This reduces the number of cables running from the DCS control cabinet to the workshop, simplifying the cable layout.