Application challenge
- Electrometers and gas leak detectors can measure extremely small current signals, so relay leakage and surface contamination can dominate the error budget.
- Mechanical relays may require a minimum wetting current and can add unstable leakage paths.
- Semiconductor switches can add capacitance and leakage that mask the signal.
Design approach
- Guard the high-impedance node and keep flux residue, moisture and fingerprints away from the insulation path.
- Select relays by measured insulation resistance under the final humidity and temperature range, not only by catalog typical values.
- For microvolt-level sensor signals, consider low thermal EMF relay construction and symmetric copper routing.
- Place the relay close to the guarded node to minimize board leakage and capacitive pickup.
Engineering caution: catalog ratings are component-level references. For high-voltage, medical, EV, PV or ATE systems, verify creepage, clearance, leakage, thermal rise, EMC and lifetime in the finished equipment.
Related MiRelay series
HVFR-HI style high-insulation relays are suitable for pA/fA switching and high-impedance front ends; low thermal EMF designs are used for microvolt sensors.
Series mentioned: HVFR-HI high-insulation relays, BT low thermal EMF relays