How to use the 3051 differential pressure transmitter for measuring negative pressure, and how to set up the 375 handheld controller? Clarify doubts!
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Question for assistance: There are 3051 differential pressure transmitters (non-gauge) that need to be used for measuring the negative pressure in flues, with a measurement range of 300 Pa to -1700 Pa. The original method involved connecting the pressure conduit to positive pressure while negative pressure was connected to the atmosphere; the gauge settings were LRV at 300 Pa and URV at -1700 Pa. The control room DCS performs inversion, with the DCS range matching that of the gauge. Currently, the header displays both values of -109Pa/15.*%, and the output is 6.***mA; the DCS in the control room shows -437Pa. All cards are functioning properly and delivering normal outputs, but there is a problem after entering FTA mode, preventing normal operation. How to resolve this? Also, regarding the header settings, the LRV is set to 300 Pa and URV to -1700 Pa. In my opinion, it should be LRV at -1700 Pa and URV at 300 Pa; the DCS should make no adjustments and display the values as they are. I’m not sure if this method is correct! I asked the experienced worker, and he said that this approach was designed by the original manufacturer, so it cannot be changed; there’s nothing that can be done if it’s not normal. It really frustrates me; I want to figure out exactly how to make it work properly.
Firstly, it’s not clear what FTA means. Secondly, it’s unclear why a differential pressure gauge was used instead of a single-flange gauge for indicating gauge pressure; this seems like a waste. Additionally, the lower limit is positive, which suggests that it might be a double-flange gauge experiencing positive drift issues. But your description mentions pressure transfer tubes. . It seems there are no capillaries either; so is the pressure difference in this air duct very large?
The inverted value of DCS most likely indicates that the range setting of DCS is different from that of the gauge. . To facilitate the observation and recording of process parameter values
The range mentioned by the poster is the same; the DCS value is inverted. . . But the apparent value of over -100 with an output percentage of around 6 does not correspond to the -400 shown on the DCS, as you mentioned. . . .
FTA is the last card in the DCS controller; the process is AI node – safety barrier – AI card – FTA – CPU of the DCS controller, and that’s the entire sequence. Differential pressure transmitters are much cheaper than single-flange pressure transmitters; those without capillaries have pressures in the range of -1000 Pa to 200 Pa, and they come with interlocks
Bro, the header output is an analog signal; the current value is 6.** mA and the output percentage is 15.**%. The reason it doesn’t match the values displayed by the DCS is that this gauge is used as a control instrument for the flue damper, and due to this mismatch the interlock function doesn’t work, which is why I’m going to deal with this gauge. I also want to match it; that would be enough. However, I don’t understand what the plan provided by the design institute meant back then, so I don’t know where to start.
The solution to this issue is currently focused on the DCS side; other issues can be addressed later. The on-site meter’s output corresponds to the display, and it has nothing to do with 375. As for the 375 setting. The 3051 series is everywhere. It’s everywhere if you search on Baidu. . . .
The reason for setting the table header in this way is probably that it allows for the reflection of the operating trends of the air ducts. . . The air duct operation mechanism is unclear; it is presumed that there is positive pressure when it is not in use, while negative pressure tends to be at high levels when it is in operation. Is it set up this way for that reason? So here’s the problem: DCS and the instrument panel state that a consistent range should be set, but yet the negative value of the output is taken – this makes no sense. . . . .
“Personally, I think the LRV should be -1700 Pa and the URV should be 300 Pa; the DCS should make no adjustments and display the values as they are. I’m not sure if this method is correct! ”Personally, I don’t see any problems with your approach; no potential issues can be identified. It can only be said that your master is either too dogmatic or afraid of taking responsibility. If there’s a problem, just say, “It’s set by the manufacturer; go talk to them.” Actually, we encountered the issue you mentioned regarding the negative pressure in our pressure relief tower; I don’t know how to reverse this situation either. However, our system settings do not allow the lower limit to be higher than the upper limit. I decided to go all the way and changed the range of the gauge header to -40kpa~10kpa; the settings on the DCS were adjusted to match those of the gauge header. It has been in use for two years without any problems at all.
It seems like it’s better to take action and give it a try; that way, analysis will be much easier
I also think that at -109 Pa, which corresponds to 20.45% of the operating range, the output current should be 7.272 mA. Is it intended for use outdoors? In the transmitters we used outdoors in the past, unexpected failures occurred; there was water on the circuit boards of those transmitters, and no cause could be found after thorough investigation