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The CALM-1 and the CALM-2 Motor Control printed circuit boards (PCBs) are simple circuits used in caliper tools to control the opening and closing of the caliper arms.
The CALM-1 motor control PCB is based on an old SIE circuit. It does not utilize a relay, but instead ingeniously uses the lower limit switch to hand off power to the tool electronics once the arms are fully open. This design is a marked improvement over other "relayless" designs and is the perfect retrofit in cases where a relay is undesirable, or has burned out and a replacement is not readily available. The usual scheme is to open with positive power, then power is automatically handed off to the electronics section when the arms are fully opened; the arms are closed with negative power. The CALM-1 PCB mounts on two (2) inch centers.
The CALM-2 motor control PCB is based on an old GO / GOI / WR circuit. It utilizes a high coil resistance relay to make the selection between opening and closing the arms with over-voltage, and powering the tool electronics package. The usual scheme is to open with negative power, then close with positive power (the opposite arrangement is easily implemented by simply changing the polarity of two diodes). The CALM-2 PCB mounts on two (2) inch centers.
The CALM-1 and the CALM-2 PCBs can be used to upgrade tools, or they can be used in new tool construction. These boards use readily obtainable components, which parts will continue to be available for many years to come, and they use convenient turret terminals for wiring connections.
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