Strange. The Honeywell ST700 differential pressure transmitter does not show a corresponding relationship between current and differential pressure once it is connected to a three-valve manifold with an orifice plate
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The water treatment workshop has three meters. After connecting the three-valve assembly, it behaves as if it’s broken: the differential pressure and current values do not match. That is: 0.1 kPa will also show 5 mA or higher. Even negative pressure shows 5mA. The scale differential pressure range is set at 20 kPa. The software for connecting to the computer is the same as that used with the handheld controller. (As shown in the figure) These three differential pressure transmitters are placed on an iron frame. As shown in the figure: (The actions that have been taken so far are as follows: ① A good transmitter was replaced, and the same problem occurred after installing the pressure tap; ② Opening the red balance valve also results in zero reading and normal current output. ③Powering it off from the on-site DCS didn’t work, and using the 5-24V output from my power bank also didn’t help. ) ④ Contacted Honeywell to report that a certain device was leaking electricity and had issues with grounding, etc. But adding insulation and improving grounding (which are already placed on the ground or walls) is useless. I seek advice from the experts. Why on earth are we looking? At the moment, there really is no solution whatsoever.
This post was last edited by tiger2010 on 2022-3-14 at 17:13. It’s better to choose a different brand; I’ve encountered quite a few problems with differential/pressure transmitters and temperature transmitters of this brand, all showing similar issues. In such cases, it’s best to switch to another brand. And what do you mean by the power bank? Is it really just a power bank for everyday use?
Yes, I have a 5V to 24V power cable. It has a USB port, which can be used to connect to a power bank or directly to a computer’s USB port. It can power the transmitter.
What type of 5V to 24V power cable is it? Are there any photos? Doesn’t this kind of cable have a limited driving capacity? Have you tried using a dedicated 24VDC switching power supply or voltage regulator?
This post was last edited by brevon on 2022-3-15 10:40. A strange question
It’s okay; it’s just a DC-DC power converter that converts 5V to 24V. You can find plenty of them by searching online. The same problem is occurring currently with my power supply module and the customer’s DCS cabinet. And it’s not on this rack either; the transmitters in other locations that are connected to the cabinet and my power supply work fine. So the issue with my power supply has been ruled out.
Oh, then it’s better to just switch to another brand
Are the on-site power/signal cables compatible with the rear system cards or safety barriers? Is the wiring correct? Is it possible to try disabling the low-flow signal of the field transmitter? Also, is this device used for measuring flow rate? If so, is the square root calculation performed at the field transmitter or in the computer system?
Are you measuring flow rate? Honeywell’s differential pressure flow measurement uses square root calculation by default; you can go and take a look.
Check that the 24V negative terminal is properly grounded
This post was last edited by hxch150804 on 2022-3-16 08:35. Is this a self-made three-valve assembly, and is it used for measuring flow rate? Is this how it starts to be used? It was good before, but it doesn’t work well now? In the chemical water plant, are you measuring the flow rate of deionized water, or the intermediate product? Or something else? Typical differential pressure flow meters are equipped with a three-valve assembly and a transmitter, while it seems that yours has been modified manually. Have you confirmed that the differential pressure of the flow meter is compatible with your transmitter? Won’t it go out of range? Or is it possible that it was installed backwards? What is the form of the on-site flow meter? Orifice plate? Ba class? Still target-type?