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  • Rick

The Magical Microswitch

Updated: May 20, 2021

The patient chair is what makes sit-down dentistry possible. The ability to have the patient reclined and low to the ground allows one to perform various procedures while seated. If there's a problem with the chair movement, your ability to treat patients is impaired at least and may not even be possible.


Most chairs have multiple points of control: buttons or touch pads on the chair itself, a touch pad on the delivery system, and a foot control on the floor are all possible points of controlling chair movement. If there's a problem with chair function and you have more than one input (control), use a different control to see if function is restored. Buttons and touch pads are frequently wiped down and disinfectants can get into the electronics causing them to fail. Smooth touch pads are better than older style buttons or switches at keeping the electronics safe from liquids, but they can still be damaged by disinfecting.


If multiple inputs fail to function (or if you only have one), you'll want to check other components. The controls you use are generally simple switches that trigger a signal from the circuit board that then controls electricity to a hydraulic pump or electric motor (depending on the make and model of your chair). The range of motion is controlled by limit switches, these are switches that cut power off when the chair moves to its maximum or minimum range of motion. There is also a limit switch to prevent anything from being crushed beneath the chair (safety switch) which is usually tied to a moveable cover on the underside of the chair mechanism. If the chair will go up but not down, a failed safety switch is a strong possibility.


The safety switch is a specific micro switch installed on most chairs and has been a staple for decades. The safety switch stops the chair if it impacts an item below it. This prevents damage to the item, the chair, or personal injury (if a person or body part is under the chair).


Most safety switches will simply stop the chair base from moving down, many will completely deactivate the chair, however. If your chair just won't move down, you almost certainly have a problem with your safety switch.


Most boards have LED indicators or displays to indicate a signal to or from the board and from the limit switches. This helps diagnose the source of a problem should function cease. You can also use a multi-meter to check for continuity of various components (like the control pads or limit switches). Check your circuit board if you suspect an electronic issue with your chair.



Subscribers can reach out to the author with the specifics of your chair (make and model) for diagnostic assistance.

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