Safety switch with imbalance test

A method comprising:

• measuring a strain voltage across terminals of a strain gauge, the strain voltage representative of an amount of force on the strain gauge;
• measuring a test voltage across the terminals of the strain gauge while a test resistor is connected in parallel with a resistor of the strain gauge, the test resistor connected while measuring the test voltage and disconnected while measuring the strain voltage;
• calculating an average strain voltage from two strain voltage measurements, the strain voltages measured preceding and after the test voltage measurement;
• and
• determining a difference voltage, the difference voltage comprising a difference between the average strain voltage and the test voltage.

A cable pull switch system comprising:

• a strain gauge in mechanical communication with a cable, the strain gauge measuring force on the cable;
• a strain measurement module that measures strain voltage across terminals of the strain gauge, the strain voltage representative of an amount of force on the strain gauge;
• a test measurement module that measures a test voltage across the terminals of the strain gauge while a test resistor is connected in parallel with a resistor of the strain gauge, the test resistor connected while the test measurement module measures the test voltage and disconnected while the strain module measures strain voltage;
• an average module that calculates an average strain voltage from two strain voltage measurements, the strain voltages measured preceding and after the test voltage measurement;
• and
• a difference module that determines a difference voltage, the difference voltage comprising a difference between the average strain voltage and the test voltage,
• wherein said modules comprise one or more of hardware circuits, a programmable hardware device and executable code, the executable code stored on one or more computer readable storage media.