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Topic Title: Can anyone share a 3-wire instrument loop sheet? Topic Summary: 3 wire gas sensor Created On: 08 August 2012 09:03 AM Status: Post and Reply |
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 08 August 2012 09:03 AM
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I've never worked with 3 wire instruments before so this is a new one to me.
I'm installing 3-wire gas sensor's in a haz area that will go direct into our siemens S7 PLC (iSP haz area I/O). Apparently the loop power is not enough so i have to supply the sensor with external power and use a 4-wire AI card abd set the sensor as source and not sink powered. Has anyone got a loop of how this should be wired? Thanks |
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08 August 2012 02:26 PM
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The ones i have used have:
3 wires or connections +v (Brown wire) positive from power supply. sig (Black wire) signal wired into input of PLC I/O. 0v (Blue wire) 0v from power supply. Not sure about the wiring of a IS module from Siemens but a would guess that the 4 th terminal should be tied to either 0v or signal. Best of luck. John |
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15 August 2012 04:01 AM
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I've never worked with 3 wire instruments before so this is a new one to me. I'm installing 3-wire gas sensor's in a haz area that will go direct into our siemens S7 PLC (iSP haz area I/O). Apparently the loop power is not enough so i have to supply the sensor with external power and use a 4-wire AI card abd set the sensor as source and not sink powered. Has anyone got a loop of how this should be wired? Thanks 2 of the wires provide power to the instrument +24V DC & 0V DC. The third wire provides the current drive to the card 4-20mA. So you are correct that the instrument is the source. Make sure that both the instrument and the I/O card use the same power supply. |
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28 August 2012 09:22 AM
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Hello gadge,
Additional criteria to be satisfied with the proposed loop is that Intrinsic Safety (or the agreed concept of explosion protection) is achieved. |
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14 October 2012 08:28 AM
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Thanks for replies. Didnt get notification for some reason, anyway..
I set the gas sensor up on the bench, with a 24vdc supply going to the sensor across + and 0V, and for the signal out i doubled up on the 0V and 4-20mA +. I was getting the correct mA reading on the multimeter. Good point about using the same PSU, i was going to use a seperate one, only because i dont think there are any spare ways off the PSU supplying the ET200 iSP PLC. |
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17 October 2012 02:51 PM
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Just a note to say beware that you do not infringe the I.S. integrity of the device. I would carefully read the atex cert of the gas sensor and also explore the possibility of using a galvanic device driver.
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17 December 2012 07:10 AM
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3-wire connections means It's +24 , 0 Vdc & signal (+)
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