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analog voltage drift with scxi 1100
Setu
Member
02-18-2002 05:35 PM
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Hi all,
I am using SCXI 1000 with SCXI 1100 module and SCXI 1300 terminator. I am using these to measure two loadcell and three deflection. During testing the setup I came across a slight problem, and can't seem to find a soultion. Thus, I am hoping someone can help...
The loadcell are calibrated such that a external digital control can be used to control/zeroing and other purposes. These digital control can simulate a load of 10kN at the flick of a switch for testing software. This means a constant DC voltage is comming into the SCXI 1300, I check that with a multimeter. But in my software (and also using the test channel option in MAX) the load drops off 2 to 3 kN every 10 to 15 seconds and gradualy goes back to 10 which
indicates to a voltage drop of about 1 to 1.5 volts. I cannot figure out why this is happenning. I used the same loadcell with our old system (called datataker) and did not see any voltage drop.
I cannot see what I am missing. Do I connect the signal to ground reference. The signal is connected in differencial mode and how do I ground reference it in SCXI 1300? Or am I not using the right module/terminator for reading analog voltage comming froma loadcell? I also have 1122 module with 1322 terminator I can use, which I will try soon.
As you may have guessed I am very confused. I will appreciate any thoughts/suggestion/inputs/answers.
Regards,
Setu.
I am using SCXI 1000 with SCXI 1100 module and SCXI 1300 terminator. I am using these to measure two loadcell and three deflection. During testing the setup I came across a slight problem, and can't seem to find a soultion. Thus, I am hoping someone can help...
The loadcell are calibrated such that a external digital control can be used to control/zeroing and other purposes. These digital control can simulate a load of 10kN at the flick of a switch for testing software. This means a constant DC voltage is comming into the SCXI 1300, I check that with a multimeter. But in my software (and also using the test channel option in MAX) the load drops off 2 to 3 kN every 10 to 15 seconds and gradualy goes back to 10 which
indicates to a voltage drop of about 1 to 1.5 volts. I cannot figure out why this is happenning. I used the same loadcell with our old system (called datataker) and did not see any voltage drop.
I cannot see what I am missing. Do I connect the signal to ground reference. The signal is connected in differencial mode and how do I ground reference it in SCXI 1300? Or am I not using the right module/terminator for reading analog voltage comming froma loadcell? I also have 1122 module with 1322 terminator I can use, which I will try soon.
As you may have guessed I am very confused. I will appreciate any thoughts/suggestion/inputs/answers.
Regards,
Setu.
02-19-2002 12:10 AM
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Hi all,
Just a note to all that I have managed to find the missing link with considerable help from others. The voltage inputs were not referenced to ground and I was missing a link between the DC negative and Chasis ground.
Done that and the system works fine. Thanks to all who were taking time to answer my query and to you sir for reading this.
-Setu.
Just a note to all that I have managed to find the missing link with considerable help from others. The voltage inputs were not referenced to ground and I was missing a link between the DC negative and Chasis ground.
Done that and the system works fine. Thanks to all who were taking time to answer my query and to you sir for reading this.
-Setu.
Annette Perez
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02-19-2002 11:54 AM
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Setu,
If you were using a terminal block SCXI-1303, the negative connection of each channel on the terminal block is already wired to ground through a bias resistor. But, since you are using SCXI-1300, you will need to add that bias resistor externally.
In general, if your transducer is floating with respect to ground, bias resistors will help grounding that signal to the chassis ground. If, however, the transducers that you use in your application are not floating, but connected to a ground point, then:
1. If you are using the SCXI-1303, disable the ground-referencing circuitry on the terminal block.
2. If you are using the 1300, do not wire any bias resistors to ground.
All these steps are neccessary to prevent the creation of ground loops
.
Good luck with your application.
If you were using a terminal block SCXI-1303, the negative connection of each channel on the terminal block is already wired to ground through a bias resistor. But, since you are using SCXI-1300, you will need to add that bias resistor externally.
In general, if your transducer is floating with respect to ground, bias resistors will help grounding that signal to the chassis ground. If, however, the transducers that you use in your application are not floating, but connected to a ground point, then:
1. If you are using the SCXI-1303, disable the ground-referencing circuitry on the terminal block.
2. If you are using the 1300, do not wire any bias resistors to ground.
All these steps are neccessary to prevent the creation of ground loops
.
Good luck with your application.
