MTS Material Test Systems - Manual (Page 66)

Note:
The following steps are provided as a guide to the servo loop adjustments. Adjustment of these controls
will vary depending on the test specimen and the components of the test system (for example, test
fixtures, type of feedback, hydraulic components, etc). As operator experience is gained, the steps
can be modified to achieve the desired response.
1. Set the Span control to zero.
2. Set up the oscilloscope to monitor the program command and load signal. Make the appropriate adjustments
for amplitude and time base on the oscilloscope.
3. Set up the selected programmer to output a low-frequency (1 Hz to 2 Hz) waveform. In most test situations,
a square wave can be used. It will provide the most broad-band, informative response.
When setting up the test system for a sensitive specimen, use a triangle or ramp waveform. A triangle or
ramp waveform should contain sufficient frequency and provide sufficient response to optimize tuning
without damaging the specimen.
4. Start the program.
5. Slowly adjust the Span control for a small percentage (5% to 10%) of the maximum amplitude of the actual
test program.
Caution:
The following steps might cause actuator oscillation and unstable system operation.
In some systems, actuator oscillation and unstable system operation can cause specimen or
equipment damage.
If sustained oscillation is not acceptable, perform the following steps instead of steps 6 to 10.
1. Increase Gain (P) to get an overshoot without ringing. 2. While watching the rate of decay
oscillation, add Rate (D) and then readjust Gain (P) and Rate (D) iteratively. 3. Verify the
system response at different amplitude levels. Readjust the servo loop controls as necessary.
6. Increase the Gain (P) adjustment to achieve an overshoot
7. Adjust the Rate (D) control counterclockwise to eliminate the ringing.
8. Increase the Gain (P) adjustment until ringing is observed.
9. Adjust the Rate (D) control to eliminate the ringing without excessive overshoot.
10. Adjust the Rate (D) control clockwise to eliminate any overshoot.
11. Repeat steps 6 through 10 to achieve the desired response.
12. Verify the system response at different amplitude levels by increasing the Span control setting. These
amplitudes should represent at least 10% of the maximum test program amplitude. Readjust the servo
loop controls as necessary (steps 6 through 10).
13. Stop the program.
14. Increase the Reset (I) control until the zero reference begins to waver. Decrease the Reset (I) control until
the signal stabilizes.
15. If desired, select displacement for test control.
66 MTS Material Test System Operation
7.0 Operation