A cam follower micro switch has two parts to evaluate: the mechanical motion that operates its actuator and the electrical contacts that change state. Knowing how to test a cam follower micro switch means checking those stages separately, then confirming that they work together consistently. This procedure covers the switch and its cam-follower actuation, not the full machine or its control system.
Before using continuity or resistance mode, shut down and isolate the relevant circuit. Lock out the equipment where applicable, account for stored energy, and verify that power is absent. Energized tests or machine operation require suitable procedures and qualified personnel. Never force the follower beyond the switch’s specified travel. The switch’s exact terminal arrangement and operating limits must come from its markings or applicable documentation, not assumptions or generic values.
How to Test a Cam Follower Micro Switch Safely
Set a clear boundary around the inspection: the switch, the cam, and the follower motion that actuates the switch. Do not treat a contact measurement as a test of the entire machine. Other connected components can affect readings, and a machine-level fault may have causes outside this procedure.
Shut down and isolate the circuit before measuring resistance or continuity. Follow applicable isolation procedures, lock out where required, and account for stored energy. Verify that the circuit is de-energized using suitable equipment and procedures before connecting the meter. If absence of power cannot be established, do not proceed with an unpowered contact test.
Use suitable electrical test equipment and select continuity or resistance mode only after confirming isolation. Keep movement controlled and within the switch’s specified travel. Do not push harder or farther in an attempt to make a reading change; excess force can obscure the test and exceed the documented limit. If the test would require energized operation or a change to machine guarding, stop and refer it to qualified personnel.
Inspect the Cam, Follower, and Switch Before Measuring
Start with a visual and mechanical inspection. Check whether the switch is mounted securely and whether the cam aligns with the follower. Look for debris, visible wear, contamination, damaged housing, loose terminals, or signs of overheating. Do not dismantle sealed components as part of this inspection.
With power isolated, assess whether the follower moves freely through its intended range and returns without apparent binding. Observe whether the cam reliably reaches and releases the follower during the normal movement being tested. A cam that misses the follower, or a follower that cannot move freely, can prevent a contact change even when the electrical contacts themselves are functional.
Keep mechanical observations separate from electrical conclusions. Restricted movement, poor alignment, or unreliable engagement is evidence of a mechanical issue to investigate; it does not by itself establish the condition of the contacts. Likewise, a visible defect or loose terminal is a finding to record, not a substitute for a controlled contact check. Do not adjust the cam or replace the switch as part of this test.
Identify Terminals and Record the Resting Contact State
Identify the terminals from the switch markings or applicable documentation before attaching a meter. In general changeover terminology, COM means common, NO means normally open, and NC means normally closed. These terms do not establish where terminals are physically located or prove that a particular switch uses a given arrangement. Verify the exact device schematic rather than assuming terminal positions or configuration.
With the circuit isolated, connect the meter to the identified contacts and record their state while the actuator is unoperated. Note the meter mode, the terminals checked, and the observed continuity or resistance indication. Treat this as the baseline for comparison during follower movement. Do not infer a specific expected reading unless the applicable switch information provides it.
An in-circuit reading can be misleading because parallel paths may affect the measurement. If connected circuitry prevents a clear result, a qualified person may disconnect a lead or otherwise isolate the switch, but only when safe and appropriate. Preserve the terminal identification and record what was isolated so the later reading is not mistaken for an in-circuit result.
Test Contact Changes Through Follower Travel
Monitor the identified contacts while moving the cam or follower slowly through its normal actuation direction. Keep the movement controlled and within specified travel. Record the point at which the contact state changes, then continue only as needed within the documented limit to observe the response. During release, record when the contacts return to the unoperated state.
The movement from the free position to the operating position is called pretravel. The distance or angle from the operating position to the releasing position is movement differential, also called differential travel. Release force is the force or torque to which force on the actuator must be reduced to permit the contacts to return to the unoperated position after operation. These terms describe distinct parts of actuator behavior; use the specific switch documentation for any applicable values rather than applying generic limits.
Repeat the slow movement through several cycles. Note whether the contacts change and return consistently, and record any missed changes, chatter, delayed release, or inconsistent indications. Also note whether the cam engages the follower on each cycle and whether follower movement remains free. The test is about repeatability across both stages, not merely whether the meter changes once.
Interpret Results Using the Switch Specifications
Use the observations to separate mechanical and electrical failure paths. If the cam misses the follower, alignment appears poor, or follower movement is restricted, the mechanism may not be providing the intended actuation. Investigate those observations before concluding that the contacts have failed. A missed engagement or binding follower can explain an absent or inconsistent contact change without proving an internal electrical fault.
If the follower moves freely and the cam engages it consistently, but the contact state does not change or return reliably, consider a contact or terminal problem. Confirm the result with isolated measurements when that can be done safely and appropriately. An in-circuit reading alone may not identify the switch’s condition because other connected paths can affect it.
Compare observed operating and release behavior with the documentation for the exact switch. The operating point is where operation occurs, and the releasing point is where the contacts return during release. Do not substitute generic travel or force values, or push beyond rated travel to force agreement with an expected result. Without applicable switch specifications, report the observed behavior and leave compliance with operating limits unresolved.
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When to Stop Testing
Stop if the circuit cannot be safely isolated, stored energy cannot be addressed, or the mechanism is damaged. Stop as well if obtaining a result would require live testing, machine operation, or a change to guarding. Energized testing and machine operation require suitable procedures and qualified personnel; do not extend an unpowered switch test into an improvised machine test.
The findings should preserve the distinction between mechanical motion and electrical response. Record the inspection observations, identified terminals, resting contact state, observed change and return points, repeatability across cycles, meter mode, isolation conditions, and any lead or connection isolated. This record supports further diagnosis without claiming a cause that the observations do not establish.
The practical conclusion from how to test a cam follower micro switch is limited to what was observed: whether the cam engaged the follower, whether the follower moved as expected, and whether the identified contacts changed and returned consistently under the test conditions. Compare those observations with the exact switch documentation. If safe isolation is uncertain or the results require energized machine testing, stop and involve qualified personnel.
Sources and references
- Defense Logistics Agency ASSIST: MIL-PRF-8805K: Switches and Switch Assemblies, Sensitive, Snap Action, General Specification For
- Wikipedia: Miniature snap-action switch