MTS DCPD Measurement System - Manual (Page 36)

Operation
Operation during testing is primarily controlled through software and the Test Controller. Refer to your
software and controller documentation for additional information.
Manual Controls
Description Item
Current Set: 10-turn control and Local/Remote selector switch. 1
Gain: X1/X10 selector switch. 2
LPF (low pass filter) 50HZ/300HZ selector switch. This switch should typically be
set to 50 HZ. 3
Manual operation is somewhat empirical and depends on specimen size and material. It is suggested that
you initially use these controls on dummy specimens and monitor results during simulated testing to achieve
familiarity with these controls.
Current Set and Gain
In most cases, the current is controlled remotely (Local/Remote switch set to Remote). With the
Local/Remote switch set to Local, the current is controlled by the 10-turn potentiometer.
The current gain goes from zero Amps (dial setting 000) to about 20 to 25 amps (dial setting 1000). A dial
setting of 500 would be about 10 to 12 amps.
Bigger specimens need more current to measure specimen resistance (Potential Drop) effectively. The
typical current for a room temperature w =2.0 inches B=1.0 inches aluminum specimen is about 10 amps.
Thinner specimens need less, thicker specimen need more.
The typical gain for the aluminum specimen mentioned above us about 50,000 times gain. The preamplifier
is 5000 times gain. The Gain X1/X10 switch can add another 10 times gain on top of the 5000 times gain
the preamp provides to raise the gain to 50000 times gain. Some small (thin) specimens will not need the
additional 10 times gain.
About DCPD Settings
What you are trying to achieve with these adjustments is a good feedback signal that represents crack
growth to the controller.
36 | DCPD Measurement System
Operation