The matrix relays have specific voltage and current ratings and can be damaged if these parameters are exceeded – this can typically happen accidentally during test development and debug. The damaged relays can exhibit a variety of failures including:
- Permanent or intermittent open/short circuits
- Variable path resistance
These are often very difficult to diagnose as they can mistakenly connect signal buses together causing unpredictable UUT behavior. |
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Historically, complex switching systems on platforms such as VXI and Pickering’s GPIB products have included a degree of self test for the relays. But in PXI and LXI, the industry has not included self test on switching because of the compromises introduced on density and cost when implementing previous self test architectures. As an alternative, some PXI switching solutions include relay operation counters to attempt to predict when a relay will fail. Although it may be helpful to know how intensively a relay might be being used it is not on its own a good indicator. The disadvantages are:
- Load conditions alone can impact the relay operating life by more than three orders of magnitude
- Using the measure as a predictive maintenance tool (replacing relays when they have operated a number of times) can easily degrade the reliability of a switching system because of the disturbance that relay replacement causes to adjacent devices (not just relays), the risk of introducing a relay with “infant mortality” and even the potential for damaging the PCB when the change is made, especially if the relays are surface mount devices
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