Is there a limit on the length of the transmitter output cable?
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Is there a limit on the length of the transmitter output cable? For ordinary temperature transmitters and pressure transmitters used in conjunction with the analog input modules of DCS/PLC (which supply power to the transmitters), what type of cable is suitable? Is there a length limit if the distance between them is large?
It has a limited value; generally, cables with a current range of 4–20 mA cannot exceed 1 km in length
What comes out of the transmitter is usually a standard electrical signal. For long-distance transmission, shielded twisted pair cables should be used, and it’s better to employ current signals for transmission as this is more reliable! When transmitting analog signals, there are certainly requirements regarding the length of the cable: one reason is to prevent signal attenuation, and the other is to reduce interference along the way
The power supply in the control room is assumed to be 24V. The minimum voltage for the power supply of field instruments is taken as 24(1-10%). By dividing the allowable circuit voltage drop by 20mA, the allowable line resistance is determined. By dividing this allowable resistance value by the resistance per meter of wire, the length of the wire can be calculated; dividing by 2 then gives the maximum distance the cable can span.
It has a limited value; generally, cables with a current range of 4–20 mA should not exceed 1 km in length. This is done to prevent signal attenuation as well as to reduce interference along the cable length
The cable type commonly used is KVVPR, but the length should generally not exceed 1000 meters. This is not so much due to signal attenuation; the transmitter outputs a constant current, and too long wires can cause excessive load on the transmitter, leading to unstable or incorrect output
There are limitations, but repeaters can be used to amplify the signal.