CompactLogix 1769-IF8 connection

[wsy_nte 0]

Hi... I have to connect 3 voltage 0-10vdc inputs (from 3 voltage divider - see attach, diffential connection) to 1769-IF8. Configure the 1769-IF8: input type 0-10vdc, data format is engineering units and scale it to 0 to 3000 rpm. The reading is not stable, always fluctuate about 10 rpm. How to solve this problem? I use SCL instuction to scale the inputs. Any idea or suggestion? Thanks. James Voltage_divider.doc

[TimWilborne 108]

Is the 0-10 VDC fluctuating? Do you want to fix it(wiring) or do you want to hide it(program)?

[wsy_nte 0]

Yes 0-10vdc fluctuating. If possible I want to fix the wiring. How about my wiring? If wiring is ok and could you advice me the code (rslogix 5000 code) to make it stable? Thanks. James

[Bill Linne 0]

If the 0-10vdc is usually stable, but becomes unstable when connected to the input module with the other signals, you may want to try a loop-powered isolator. These are commonly available, and have solved many a "cross-talk" problem for me in the past. Another thing to check for is the possibility of AC voltage riding on your DC inputs. A small capacitor across the input will usually eliminate this problem. Bill