Guard rings in strain gauge measurement
Hi... Can you please tell me as to what is a guard circuit used in bridges?..........................................
Mail from SN
The very high impedance amps for bridge circuits have inputs in tera ohms and bias in pico amps. The sensitive bridge circuits must be able to detect a 1 uV difference when a 100 gm weight is placed on the cantilever. So it is very sensitive.
The power lines and other logic lines close to chip high impedance pins may leak pico amps to nano amps of currents, humid-air or PCB contamination or power pins being too close, the leakage currents may show as full scale reading without input.
The guard rings around these sensitive pins or shielding will act as return paths for the leaking nano amps.Even ionic discharge from a sharp pin with high voltage can imbalance bridge. As it is like an Electrometer.
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