MTS Series 793 Application - Manual (Page 437)

Auto Offset Process
MTS MultiPurpose TestWare® Other Process Descriptions 437
About Feedback Signal Offset
The Auto Offset control in the Station Manager application zeros the output of
the conditioner without shifting the electrical zero reference of the conditioner.
An auto offset can be applied to the current control feedback with station
pressure applied.
For example, suppose your LVDT output is 1 cm when the actuator is at its null,
midstroke position. You can compensate for this positive LVDT output by
offsetting the feedback signal –1 cm. The actual displacement value (Current
Value) is now zero.
Usable range Because the range centers around the calibrated electrical zero of the sensor, an
offset limits the usable range in the direction you shift it. For example, in a ±2 cm
range, offsetting the signal -1 cm from its zero position results in control ranges
of +1 cm on the positive side and –3 cm on the negative side.
Offset considerations Consider these items before offsetting a feedback signal:
• Offset alters the feedback signal used by the digital (PIDF) controller and is
included in the closed-loop control calculations.
• Offset cannot be used to clear interlocks tripped by signal saturation.
• Offset is limited to ±½ the current full-scale range.
• The usable range is limited in the direction that zero is offset.
Conditioner
Controller/Application
Sensor
Voltage
A/D
Electrical Zero*
Gain
Offset
The offset applies to the feedback signal.
You specify the offset in engineering units.
Conditioner
Voltage
Digital
Signal
*Electrical zero is only available on certain
types of conditioners.