Issues with connecting field instruments to safety barriers
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At the site, the three-wire instruments are connected to the cabinet and then to the AI safety barrier (the three-wire safety barrier of MTL). However, the instruments at the site do not function (their displays show no output, indicating that they are not receiving power). When the safety barrier is measured without the instruments connected, it shows a voltage of 25V, while when the instruments are connected, the voltage is only 4V. Additionally, a 24V power supply is connected directly to the field instrument, which then displays information. What is the reason for this? The field instruments are intrinsically safe instruments.
It is best to check whether the detailed specifications of the on-site instruments and safety barriers match; even though they are both three-wire systems, this does not necessarily mean they will be compatible
Let’s take a look at the maximum output power of the isolator and the power of the 3-wire instruments on site… It seems that the power of those 3-wire instruments is too high, so the isolator isn’t able to handle it
Based on the description, it seems there is a power mismatch – the power output by the safety barrier is less than what the instrument requires. It cannot drive the instrument.
For safety reasons, it is better to use two-wire instruments for intrinsically safe circuits; three-wire instruments have varying power consumptions, and a slightly higher power level may prevent them from functioning properly.
Is this a newly added point or was the existing one damaged?
Wrong wiring. The power, signal, and ground wires of three-wire instruments must pass through a safety barrier to be connected to the system. The power supply and ground are incorrect, and the on-site meter does not display anything. The signal and ground are incorrect; the signal cannot be introduced into the system.
Thank you all. I consulted the manufacturer, and it seems that the power of the safety barrier is not compatible with the field instruments.
New issue: the manufacturer says the safety barrier doesn’t have enough power
Thank you. It must be this problem
1. Consult the safety barrier manufacturer； 2. Verify whether the wiring is correct ； 3. It is rare to encounter intrinsically safe three-wire instruments; it is necessary to determine whether the instrument on site is intrinsically safe or explosion-proof. If it is explosion-proof, it is recommended that the signal lines be fed through an isolation barrier while power supply is provided separately.