1/5/2021 3:11 AM | |
Joined: 3/28/2010 Last visit: 10/4/2024 Posts: 1058 Rating: (213) |
1. > "What you mean by Uvo the AI 24V power supply (+)? A 2 wire, loop powered field device gets its power from an external power supply wired in series with the 'loop', as shown in the drawing in the link or the attachment. https://postimg.cc/7CWd8kS9 The AI terminal marked Uvo is a +DC power supply output. The text above it says, "You can also supply the 4-wire transmitter via the encoder supply terminal Uvo". It is labeled "sensor supply" Whether it is used to power a 2 wire, loop powered field device or a 4 wire device, or nothing, depends on how it is wired to the field device. If it is wired in series with the analog output, it is a loop power supply for a 2-wire device. If it is wired to separate power terminals, then the field device is a 4 wire device. If it is not used, then some other power supply is providing power to the field device. - If that other power supply is wired in series with the analog output, it is a loop power supply for a 2-wire device. - If that other power supply is wired to separate power terminals, then the field device is a 4-wire device. In the drawing, Uvo is not used; it is not connected to anything. That means some other power supply powers MU. The MU field device is shown with a Uv+ connection (+DC power) that powers the MU analog output, but UV+ is not in series in the loop it is a separate terminal, further confirming that MU is NOT a 2 wire, loop powered device, rather it is a 4 wire device. So the diagram apparently shows a 4 wire device connected to the AI card. I assume the diagram is for the AI card/module in question. (I did not provide the diagram, I am merely commenting what it seems to represent.) 2. >You mean I can connect a voltmeter across the VFD signal (-) and and AI power supply (-)? I'm supposed to read a voltage between those 2 negatives? M is the analog input (-) terminal. It might be power supply (-), but that is not shown. Any voltage between VFD (-) and terminal M [the AI signal (-)] is known as "common mode" voltage. One hopes that there is no common mode voltage between those two points. But if there is common mode voltage between those two points then the effect of common mode, depending upon the magnitude of the common mode voltage is - a signal offset, on-scale plus or minus, typically an obvious 'error'. - signal offset off-scale, plus or minus, where the signal is not even within the range of the analog input, it is off-scale high or off-scale low. - the input card smokes, is damaged and rendered unusable by the excessive common mode voltage Rather than damage an AI card, I recommend testing to see how much common mode voltage there is between those two points. Since most Ai's can handle low common voltage without an offset or damage, then I'd try connecting the field instrument as shown in the diagram: VFD (-) connected to terminal M, the AI analog input (-) and if measurement is less than 5Vdc and/or 5 Vac then I'd proceed with connecting the 4 wire device as shown and seeing whether the AI card reads the signal without a significant offset error., 3. >I don't know why ET200SP HA don't have 4-wire AI product. I'm an instrument/Modbus/4-20mA guy, with little Siemens PLC experience. My comments are based on the drawing provided and decades of 4-20mA experience. The drawing appears to show a 4-wire device connected to the AI module. Why do you think that the module is 2-wire only? |
Last edited by: danw at: 01/05/2021 03:21:40Last edited by: danw at: 01/06/2021 00:44:44 |
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