Elevator Trim jumping up and down - how to fix?

[hplevyak]

Guys,
I've gone through the procedure for calibration of my elevator trim.

I'm using a TCW Safety Trim 1-12V-2SP (2 speed) system. It's wired up per the GRT Horizon HX Trim diagram.

I configured it by going to General Setup / Flap & Trim Calibration (page 1).
1. Put the selector on the NOSE UP box, moved my trim to full nose up. Let the voltage reading stabilize for 5 secs, and then hit SET.
2. Put the selector on the NOSE DN box, moved my trim to full nose down. Let the voltage reading stabilize for 5 secs, and then hit SET.
3. Put the selection on the ELEVATOR mid position box (trim neutral), moved my trim to NEUTRAL. Let the voltage stabilize for 5 secs, and then hit SET.
4. I selected MAIN, then SAVE.

It's working ok...but the triangle Pointer is jumping up and down on the screen just slightly. It's moving up and down by +/- 1/32 of an inch. Any way to resolve this?

I'm currently using a ground power supply unit...so maybe this is the cause with DIRTY voltage coming in?

Thanks, Howard

[GRT_Jeff]

Is there enough of a voltage range? The analog inputs are not high precision. If it's just noise on the analog input, you can try enabling the digital filter. Go to the SET MENU, Display Unit Maintenance, Analog Inputs, and change the Analog Detail to "Raw data and filtering". Scroll down to the input you're using for the elevator trim and adjust the DF value with the knob. Higher DF values increase filtering but also slow the response.