On 2026-01-02 9:24 a.m., Tony Miklos via Jukebox-list wrote:
On 1/1/2026 1:35 PM, John Robertson via Jukebox-list wrote:
On 2026-01-01 6:40 a.m., karl hjort via Jukebox-list wrote:
I remember Ron Rich often pointing out that only an analog meter will catch a sloppy microswitch. Something ingrained in my tiny brain now.
I do find that my fixed range cheap DMM finds defective switches easily on the Ohms or even on the Continuity setting.
As I teach my staff, use jumper wires to hook the NO switch to the meter. Then slowly activate the switch until it just trips. Note that the resistance is in the 1 Ohm range or so. Now slowly continue to depress the actuator - if the reading bounces around the switch is usually defective. A good microswitch stays at the same reading throughout the activated state. This also works on NC side, just the opposite, read closed, slowly press the actuator, if the reading bounces around replace the switch.
I have them run this test on ALL the microswitches in a machine, it solves so many intermittent issues!
John :-#)#
John, (I think) you forgot about continuing to read the resistance as the switch is approaching the open position. (NC and NO) Quite often they get more resistance as they approach the opening state, before they click/snap.
Resistance shouldn't change on a new microswitch, or one that is working properly as you near the hysteresis point. It should be the same or within milliOhms of zero Ohms. Increasing resistance indicates a failing contact surface and time to replace - or dismantle and polish if you can.
John :-#)#