To calibrate the amplifiers to the 2.5 Amp peak output, a few of the fixed resistors on the Copley #303 amps need to be replaced. In addition, fine calibration needs to be done by adjusting the two potentiometers located on the side of the amps. The potentiometer labeled FB is used to adjust the gain (full scale current output) and the potentiometer labeled BHL is used to adjust the offset. It is suggested to run the current through a dummy motor OR power resistor in series with an inductor when calibrating the amplifiers.
It is only necessary to replace the 1st resistor (counting from the left), leaving all other resistors and capacitors unchanged. Make sure to use high quality 1% tolerance resistors. Currently shown as 262.1 k-Ohm, but anywhere form 262-350 k-Ohm is an acceptable value here (the amplifiers originally had a 49.9K resistor).
Ballpark values for the fixed resistors and capacitors in the amp chip carrier for 2.5 amp peak output are (from measurement with an ohm-meter):
262.1 k-Ohm | 48.9 k-Ohm | - | 9.86 k-Ohm | - | cap | 45.5 k-Ohm | cap | empty | 39.6 k-Ohm | 9.79 k-Ohm |
More information about the CopleyAmplifiers. -- WillP? - 20 Oct 2004
Note that the 3-Axis amp box will have an additional 3 encoders coming into (the currently 6 open pins on) header A from the stylus gimbal. These are presumably wired to the same pins on "header P" as the encoder pins coming from "header B" on this 6-Axis box.