MTS Material Test Systems - Manual (Page 48)

Table 6: Error detection level
Description Item
Program command 1
Feedback 2
DC Error 3
Time lag 4
The error detector can be preset to detect an excessive DC error. The level of acceptable DC error depends
directly on the accuracy requirements of each testing situation.
In static and low-frequency tests, error detectors are typically adjusted for levels that would stop the test when
a specimen fractures or excessive deformation occurs. However, in higher frequency tests, the instantaneous
DC error increases in proportion to command frequency and the error detectors have to be adjusted to higher
levels. This is due to the time lag, or phase shift, between the program command and system response.
Therefore, the error detectors are generally set to sense a loss of closed-loop control at higher command
frequencies.
The DC error level can also be adjusted during testing if desired. Operator experience is the best guide for
adjusting the error detectors for high frequency testing.
6.3.4.0 Calculate Upper and Lower Limit Detector Levels
Each controller contains upper and lower limit detectors that monitor the feedback from its associated
transducer. Unlike the error detectors described in the previous subsection, the limit detectors can be enabled
to shut down the test regardless of whether the controller is selected for active control.
The limit detectors can be preset to detect a specific upper or lower feedback limit. When the feedback
exceeds the preset upper limit detect level, the limit detector will (if enabled during test setup) stop the test
48 MTS Material Test System Operation
6.0 Getting Started