A strange galvanometer
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Hello everyone, it’s a new device that uses a Yokogawa flow meter. The actual flow rate is 4 L/Min, with a range of 4–20 mA; it should output 15 mA. The actual current in the circuit is 3.6 mA, and the DCS displays -0.15 L/Min, which corresponds to 3.6 mA – this is correct. I used the HART handheld transmitter to measure the line output signal, and it was 15 mA at 4 L/MIN, which matches the value displayed by the flow meter. It’s a DCS module without HART functionality; I can’t figure out what the problem is
It seems the problem might lie in the DCS module’s reading and parsing of signals. Since the flow meter can communicate via the HART protocol, when using a handheld device to measure the output signal, the data is actually read directly from the flow meter. The DCS module, on the other hand, needs to receive the correct 4–20mA current signal and convert it into the corresponding flow rate value. If there are issues with the reading and parsing functions of the DCS module, it may result in abnormal traffic values being displayed. It is recommended that you check whether the connection and configuration of the DCS module are correct, and try to recalibrate the signal transmission between the flow meter and the DCS module. If the problem persists, please contact the equipment manufacturer or technical support staff for further investigation. .
There’s nothing hard to understand; what the handheld device shows isn’t real anyway. It’s the flow meter that’s broken. Generally, replacing the 4-20MA output module will resolve the issue. Also known as connection terminals. The output module of the Yokogawa flow meter is integrated into the terminal blocks
Measure the output of the on-site flow meter and the input of the machine room DCS with ammeters once each, and that will reveal which one is the problem.
Shouldn’t these two points show the same value?
Oh, then it’s probably somewhere in the signal circuit that there’s a ground connection
This post was last edited by jlshnlhj on 2023-3-21 at 11:22. It’s the same when there are no problems; but what if the insulation in the middle of the cable is damaged, causing leakage, or if there are joints in that area and water gets in? That’s why it’s said: measure each one once, do the conversion, and then you’ll know which one is the problem.
Although the supply voltage range of the field instruments we use today is quite wide, the likelihood of an on-site indication in the event of a leakage current is relatively low. What you said makes sense as well; it’s recommended to measure the current flowing into the card’s connections to see if there is a problem with the channel.
This post was last edited by jlshnlhj on 2023-3-21 at 17:36. Measure each one once and make the conversion, and you’ll know whether it’s a DCS channel, a transmitter, or a wiring issue. Just be careful when converting: for orifice plate flow measurement, determine whether it is a DCS or whether the transmitter needs to perform a square root operation.