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| 4/26/2009 11:14 PM | |
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Posts: 7 Rating:
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| 5/26/2009 12:08 PM | |
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Posts: 173 Rating:
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1) If the sensor has 4 wires, then 2 of these are for its own power and the other 2 are for the 0/4..20mA signal to the LOGO!. Put the 500 ohm resistor across these 2 wires and then connect the negative signal lead to the LOGO! common (M) and the positive signal lead to the analog input (I7, I8 for 0BA4/5 and also possible I1 & I2 on 0BA6). 2) if the sensor has only 2 wires, then it needs to be 'loop powered'. Therefore, connect the 24V DC power supply to the positive signal lead, then the negative signal lead to the LOGO! analog input, then put the resistor across the LOGO! M line and the sensor negaive signal line to the analog input 3) MANY sensors do not like ot have more than 250 ohm in the loop (2 or 4 wire types). So then, the best way is to use a 250 ohm and do the proper scaling in the LOGO! program. 4) Also attached, some sample high quality resistors with EXACT values. Standard value resistors (470 ohm, 560 ohm or 270 ohm, 200 ohm)with standard tolerances introduce some strange scalings can make the incoming signal rather unstable because these resistors are dependant on temperature. Rather take the time to get a suitable high quality, exact value, very low tolerance resistor. Hope this helps some of you! Attachment500ohmVeryHighPrecision.pdf (757 Downloads) |
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