Hello there!
I hope some of you can help me out a bit here and point me in the right direction.
I am trying to measure a strain-gauge with the K8055 at the analog input.
The circuit is quite simple. I use a 5V source-voltage (Voltage-Regulated) which is connected to a Wheatstone-Bridge (built with 500k OHM resistors). The strain gauge is added to one arm of the bridge so the small resistance changes of it lead to a slight imbalance of the whole bridge. The output of the bridge is then used as input for an INA122PA operation amplifier.
Well to make things quick. When I measure the output of the INA122 directly with a voltmeter I get good stable readings from 0 to 5V when straining the gauge etc. However when I connect this output to the K8055 I don’t get any readings at all. And yes, I have removed the jumpers on the K8055 and I have turned the Potentionmeter to check if it was set wrong.
In fact, connecting the voltmeter and then connecting the K8055 instantly changes the measurement of the voltmeter and I can see that the moment I connect the K8055 the voltmeter readings go down to like around +/-0.5V and no matter what I do the voltage does not change. Not when straining the gauge, not when changing the amplification, nothing…
To test if the analog-input of the K8055 works, I built a simply voltage-divider circuit and connect it directly to the K8055. There I do get good readings. It is just when I use the INA122 output (millivolts and microvolts amplified to volts) that I don’t get any readings at all…
My resistors for the Wheatstone Bridge are quite big, around 500k. At that time I thought it quite a good idea to use those resistors to reduce the current of the circuit.
My question now for all you experts is …
- Can it be that since I built a bridge with 500k resistors, that the input (and output) current from the INA122 is too low to make any measuring by the K8055 possible?
- Might this be the reason why a simple lower resistance 5V input voltage divider leads to workable results?
- If that might be the reason, what is the minimum current that is required by the K8055 for good measurements? What would you aim for?
Or if I am completely thinking in the wrong direction and you have more ideas whats going wrong?
Any help is very very much appreciated! If you need more information, just ask and i will try to explain in more detail!