The flowmeter detects normal current, but the DCS system shows an open circuit? (Yokogawa CS3000 system)
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At the site, a flow meter suddenly indicated an open circuit fault. The multimeter measured the AI signal coming from the DCS (the signal from the flow meter at the site), with a value of 6.5 MA, which matched the actual flow rate; yet the display showed an open circuit condition! ? Use a calibrator to generate a 4-20MA signal and feed it into the AI current channel of the DCS; the channel is intact and functioning properly! After replacing the AI channel, the system still shows an open circuit signal! (IOP), I’m completely confused; please help me figure it out! Using a multimeter, it was confirmed that all signals from the system to the field were normal; the IOP value appeared on the system display for those signals! ? ? ? ?
Is the display normal when using the 4-20MA signal from the calibrator to feed the AI current channel of the DCS?
It shouldn’t be a problem with the channel; are you sending the signal from the tester at the field instrument or at the terminals in the control room?
Is the signaling at the site working properly? Still changing channels? Is the voltage normal?
With your IOP+, it is only triggered when the input current exceeds 20MA. Does your signal have a safety barrier?
Is it IOP or IOP-? It’s still pretty strange; I need to go over it again from the start.
The instrument is malfunctioning, and the card cannot handle the load of the instrument.
A 4-20MA signal is generated by the calibrator and fed into the AI current channel of the DCS; the channel is fully functional and normal! The issue lies after the AI channel; by using a tester to check step by step, the problem can be found quickly.
What type of safety barrier is being used, a Zener barrier or an isolation barrier? In the case of a Zener gate, ground interference could be a possibility. You can check the shielding grounding of the table and the grounding of the card.