3.4 Inhibit Shutdown
All models include an inhibit circuit that interrupts the current drive to the motor and lights the FAULT
LED. When the instrument is inhibited all external control inputs (Length In and Length Offset) are
disconnected internally and power is cut to the motor. This leaves the lever arm free to move.
The inhibit function is quite useful when attaching a muscle preparation since the arm can be pulled and
pushed on without causing any unwanted oscillations of the arm. If the system is not inhibited when the
muscle is being attached to the lever arm the instrument can sometimes oscillate in reaction to non-
compliant loading of the arm. An example of non-compliant loading is touching the lever arm with metal
tweezers.
Moving the Inhibit switch to the Stop position will inhibit the instrument. To re-activate the system simply
move the switch to the Run position. When re-activating the system the motor will be ramped to the
currently commanded position (the sum of the signal attached to Length In plus the signal due to the
position of the Length Offset knob) over a ramp with a duration of a few seconds. The FAULT LED may
remain lit for about 2 seconds while the system attempts to restart. The position detector works all the
time regardless of whether the Inhibit switch is in the Run or the Stop position. This feature can be useful
when attaching a muscle to the length controller. Use the following procedure.
1. Switch Inhibit to the Stop position
2. Turn the system power on.
3. Attach the muscle tissue to the arm and to the external force transducer.
4. Before moving the Inhibit switch to the Run position, check the Length Out signal (use the front-
panel voltmeter). Move the arm so that the reading on the meter is close to 0.000 volts.
5. Set the Offset knob to 5 on the dial and ensure that the signal connected to Length In is at 0.000
volts.
6. Switch to the Run position. The arm will move from the current position to the 0.000-volt
position and remain there.
3.5 Overload Shutdown
All models contain protection circuitry to protect the motor and electronics from various types of
overloads. If an overload is detected, current drive to the motor is interrupted and the FAULT LED lights.
After about 2 seconds the system will attempt to restart but will quickly go back into overload mode if the
condition that caused the overload remains.
When the power switch is first turned on the overload circuitry is activated. This ensures that power-on
transients are eliminated. If the motor is driven to a position outside its legal range of 10 volts an
overload will also be triggered. The length-input command must be reduced before the system will
restart. If the force at the tip of the arm exceeds maximum force an overload will be triggered. If the
motor is not connected to the electronics an overload will be triggered.
The overload circuitry is also triggered when the power switch is flipped off. Since current to the motor is
interrupted quickly, there is little or no turn-off transient in the motor when power to the instrument is
removed.
