Most test system controllers feature peak detection software. The purpose of the peak detection is to measure the maximum and minimum levels the transducers see during the test. Monitoring the signal peaks is used to verify that the desired test load levels are being achieved and not exceeded. For example if you set up the system to control the load at +/-10N at 30Hz you need a means for verifying that those levels are actually being met.
The upper/lower limit detectors look to see if the system signals exceed a set of outer limits. For example: If you are running a test is load control, and the displacement is cycling between 1 and 2mm, you can set upper/lower limits around the displacement peaks to stop the test if the peaks begin to increase or shift. As the specimen begins to fail the displacement peaks will increase because the specimen is providing less resistance to the applied load.
At the beginning of the test after the peaks are stabilized, underpeak detection can be set inside the load peak envelope. For example, if the test is stabilized at +/-10N, one can set underpeak detection at +/-9N. As the specimen begins to fail it becomes more difficult for the system to achieve the desired load levels and they eventually fall off. A correct setting of the underpeak detection can be used to stop the system at this point.
Both over and under peak detection are used to detect specimen failure while the test is running. At MDT we use all of the tools available in the control system to provide the most accurate test available and to ensure the system stops when the specimen begins failing.