Is it possible to use only three external completion resistors for all the twelve analog channels in order to connect quarter-bridge strain gages?
Thanks,
Luciana
Good afternoon Luciana,
No, it is not possible. The only option are across one channel pair as per pages 175 & 176 of the DT800 User manual.
Cheers,
Roger
Good afternoon,
I have tried the bridge configuration from figure 124 using not five strain gages as suggested, but only three strain gages. With this configuration, I have obtained half of the expected value. I have used the following command lines on the DTransfer:
2+BGI(120,4WC)
1#BGI(120,4WC)
1*BGI(120,4WC)
First, is it possible to use less than five strain gages in this configuration? Second, if yes, is there any other command line to obtain the correct value?
Thank you very much,
Luciana
Good morning Luciana,
Yes it will work with up to 5 gauges.
For how to convert from PPM to micro strain please refer to page 146 of the DT800 manual.
Cheers,
Roger
Good morning,
I followed your instructions but my problem has not been solved yet. I measured 45ppm using three active gauges in the bridge, with gage factor equal to 2. Now converting from ppm to micro strain, I have:
micro strain = (4/(23))45 = 30ustrain << 180ustrain (expected value)
Am I doing something wrong?
Thank you very much
Luciana
Good evening Luciana,
The whole structure is electrically three separate bridges.
The two bridge completion resisters forming one side of the bridge and each arm with one bridge completion resister and one strain gauge forming the other side.
So the maths becomes micro strain = (4/(21))45 = 90 ue.
But if you when you look at the overall resistance of of the circuit then you have 4 arms with a total resistance of 240 Ohms per arm.
So 1/Rt=1/240+1/240+1/240+1/240 = 60 Ohms.
This is what you put into the channel option so the dataTaker can calculate the excitation voltage.
Tip. If you put a resister that has a value of 1000 * Gauge resistance the equivalent strain is 500 ue compression.
Cheers,
Roger