The Emerson mass flow meter’s local display shows zero, while the value displayed on the remote DCS fluctuates back and forth. Could someone please help explain why this is happening?

It’s normal; current signals are analog signals, and interference can cause such issues. Try using an isolator.

The cut-off value for low flow rates inside the mass flow meter is too high; adjusting this cut-off value will solve the problem

The last edit to this post was made by 1111111 on 2019-1-31 at 07:46. “Fluctuations in the display values of the remote DCS”? 1. It is necessary to specify the frequency of these fluctuations – that is, it should be clear whether there are fluctuations several times per second or several times per minute. 2. The magnitude of the fluctuations must be clearly specified – that is, it is necessary to state what the values were in a consecutive series of measurements, such as 10 consecutive times or 20 consecutive times, and it is important to clarify the amount of variation in these \"fluctuations\". 3. It is also necessary to clearly indicate the range of the instrument – that is, to ensure that people can see the amplitude of the white fluctuations. Split line---------------------------------------- Without any data, it’s completely empty; how can anything be “explained” or “analyzed”? It’s just pure guesswork, right? :lol

It’s normal; just perform small-signal clipping

This piece of practical advice is that there is a small signal cutoff built into the meter itself; one just needs to adjust the cutoff range

Based on my experience, the first few process-related issues are whether the gas being measured is in a liquid state at room temperature The temperature is high during operation, so the gas cannot be in a liquid state; it will condense after shutdown? If so, check whether the header light is flashing yellow; if it is, see if there are any warnings, such as warning codes above 100. Next, check the temperature and density displays on the gauge head; these can be read using a handheld device or displayed directly on the gauge head. It is recommended to display them on the gauge head, as this facilitates troubleshooting in the future. Check whether the displayed temperature is below the condensation temperature of the gas, and also verify that the density is higher than that of the gaseous state. If so, it indicates that there is liquid accumulation inside the measuring tube, and the presence of both gas and liquid phases can cause fluctuations in the output. However, this issue will resolve itself once normal operation is resumed. It is likely that the flow meter’s measurement tube is not installed with its opening facing upward. The solution is to explain the reason to the process engineers; no further action is required. A complete solution involves reinstalling the flow meter so that its measurement tube faces upward, which reduces the risk of liquid accumulation. Additionally, provide heating to ensure that the gas inside the measurement tube does not condense, or replace the gas with another gas that does not condense after shutting down the system. Another option is to use a DCS switch to enable bypass operation of the instrument after shutdown. It is generally best not to alter the settings of the instrument itself, as this could backfire. Mass flow meters are relatively reliable and less prone to problems. Since Emerson’s mass flow meters are modular, any issues can be easily resolved by replacing the faulty module. However, when it comes to instrument problems, it is often easier to identify the root cause by analyzing the process first.

Low-flow signal rejection or interference

Low-flow signal rejection or interference

Use a multimeter to check if there are any current fluctuations, and then switch to the low-signal mode

The normal zero reading of the flow meter at the installation site indicates that there is no issue with the meter itself. The small fluctuations in flow rate displayed on the remote DCS are caused by slight errors during signal conversion by the DCS； This is quite normal; a small-signal resection will suffice