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Guide to testing TTS cells and amplifiers

 
When testing TTS transducers follow the procedure described. The first test is to ascertain that the amplifier is giving the correct supply voltage to the transducers.
 
All measurements can be taken on the connector terminals without disconnecting the load cells.
 
 
 
 
 
 
Depending upon the degree of load there may only be approximately 3mV change between the zero reference voltage and the loaded contribution.  If the figures above are not within the parameters shown then contact TTS for guidance.  This does not necessarily mean that there is a fault but other factors may be influencing the results.
 
Common Problems
 
Overstraining
 
If a difference exists by comparing the zero reference value between Channel A & Channel B this may indicate a cell has been overstrained. This can only be fully ascertained by removing the cell from the machine and testing it without any other mechanical influence. If the cell reverts to zero millivolts when not fitted to the machine the cell is very unlikely to be damaged and the problem is a mechanical.
 
Isolating mechanical problems
 
Most problems arise when the sensing roller does not return to its ‘zero’ reference. This comes from bad or misaligned bearing housings or poor fitting installations. The tendency is to attribute this to the load cells and in almost 99% of situations this is not the cause. Remember load cells move in minute distances to give their full scale results. If there is the slightest impediment to this movement then the cell will give out a signal reflecting this. This will be amplified and be perceived as drift in the electronics or cells. Equally if the return movement is not efficient then this will give the appearance of drifting around or hysteresis.
 
If possible get a colleague to push on the sensing roll in the direction of load and monitor the zero reference voltage either at the transducer inputs Sig + and Sig -. This should always return close to the same voltage each time. If not consider mechanical stiction as being the initial problem. The signal should remain steady when under static loading. If it is moving around this could indicate a damaged load cell.
 
Connections Detail using the DCA-10
 
Amplifier Tests
 
TTS amplifiers take a signal from the load cell and give a proportionally larger signal out. The input signal can be anything between ± 30 milliVolts which is amplified to produce a 0…10 V output proportional to the load. Although the calibration process is automatic it is very simple to isolate whether the problem may be occurring in the load cell or the amplifier by treating the two units independently.
 
Amplifier Input
The signal from the load cell will be in millivolts, refer to the testing procedure above. This can be measured across the inputs on the amplifier.
 
Amplifier Output
 
When calibrating the amplifier following the procedures shown in the respective manual there should be approximately 0mV for a no load condition and 10V for full load condition on each of the output channels. (Note: the zero reference could read anything up to ± 0.1V, 100mV depending upon system gain and this is normal).  On paired inputs the average channel is also active.
 
Amplifier Supply
 
Also check that the supply voltage is 24V DC and that where used earth connections are made.