300 SERIES USER GUIDE
23
Status Output Jumper
JP-103: 1-2 for open-drain MOSFET output, 2-3 for HCTTL output. Normal = HI (HCTTL),
or off (MOSFET), fault = LO (HCTTL), or ON (MOSFET).
Tuning and Adjustments
First we describe the operation of the trimpots on the basic amplifier, and the MB4 and
Eurocard. Next are more detailed sections on particular subjects such as tachometer
scaling, voltage-gain, and so on. For more detailed theory and practice, a list of
references is included in the appendix.
Trimpots
Balance and Feedback trimpots come on both basic amplifier and MB4 card. Current-
limit comes only with the MB4 card and Eurocard. Voltage-feedback and IR-Comp are
only installed on MB4 and Eurocards with the -V option (armature-voltage feedback).
Balance
Used to 'null' the output of the amplifier when the reference inputs are at 0V. Adjust the
pot for zero-current (or zero-volts measured between Out+ and Out-) when the input to
the amplifier is zero.
Feedback
Sets the gain of the servo preamplifier. Usually set to minimum (fully CW) in current-
mode operation for maximum bandwidth. When using tachometers, turn this pot CCW
until oscillation begins, and then back off 1-2 turns for stable operation. Adjustment of
this pot affects the response of the amplifier to a step-input.
Current Limit
Controls the peak current that the amplifier can output to the load. Fully CW the
amplifier will drive the rated peak current. As this is turned CCW, the maximum current
will gradually decrease. Useful for protecting mechanical parts when the maximum
current required by the load is less than that of the amplifiers peak rating.
Voltage Feedback
Sets the voltage-gain of amplifiers ordered with the MB4 or Eurocard with voltage-
feedback (-V) option. The gain of the amplifier is x22 with this pot fully CCW, and can
be adjusted upward by rotating this pot CW. See the following section (p.27) on voltage-
gain adjustment for more information on this trimpot.
IR Comp
Used in voltage-feedback mode with jumpers set for IR-comp. Adjusts the amount of
positive-feedback from the current-sense circuit. This feedback increases the output
voltage when drawing higher currents in the load. Because this is positive feedback, too
much of it can cause severe oscillation. When adjusted correctly the motor speed will
remain constant within several percent as the load changes without using a tachometer.
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