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SM331, 2 wire current measurement

Created by: skaruppiah at: 11/9/2008 3:12 PM (3 Replies)

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11/9/2008 3:12 PM	Rate (0)
skaruppiah Posts: 2 Rating: (0)	Hi, We have a 2 wire flow transmitter connectted to SM331 (6ES7-331-7KF02-0AB0). We have a 1K potentiometer ( 3 wire) on the flower sensor that's connetted to a transmitter and from this transmitter connectted to the SM331 by 2 wire that provide 4 to 20mA. Suddenly the PLC failed to read the flow value from this sensor. I connectted my multimeter in series with the 2 wire expecting to read 4-20mA when i vary the potentiometer on the flow sensor. But i only get 4mA and the current failed to increase when the vary the potentiometer. I installed new flow sensor ( e.g new pot and new transmitter). Same result. i only get 4mA. Can you guide me here to do more test to find the problem, could this be a faulty SM331 module? Regards, Nathan
skaruppiah Posts: 2 Rating: (0)
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11/9/2008 10:08 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Dear Nathan, I would like to know how far are the sensors away from the Input module you use? Have you checked the voltage at the inputs yet? Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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11/10/2008 1:15 AM	Rate (0)
skaruppiah Posts: 2 Rating: (0)	THis is an excisting installation and the flow sensor used to work fine all this while. The Flow sensor is around 50 meters away from the PLC. I get 24VDC in the P&F barrier in PLC Panel and i get 20VDC when i measure across the 2 wire in the transmitter mounted in the flow sensor.
skaruppiah Posts: 2 Rating: (0)	Last edited by: skaruppiah at: 11/10/2008 1:32 AM
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11/10/2008 7:00 AM	Rate (0)
Aret Posts: 2348 Rating: (264)	I would try to connect variable resistor directly to AI module (~1,5-3,3kOhm as i remember) and read code from module. Think it's module problem.
Aret Posts: 2348 Rating: (264)
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