SETTING THE PHASE:

Phase shifts are caused primarily by instrumentation and cable capacitance and inductance. In most cases it is best to adjust phase by maximizing voltage.

One possible way to determine phase is to measure your sample with a low frequency bridge like the LR400 or the LR700 (17 Hz), both are available at NHMFL, and take a resistance reading. The lock-in frequency and phase are set to reproduce this value.

POSSIBLE OVERLOADING PROBLEMS:

One cause of error and lost data is overloading of the lock-in, or the preceding pre-amplifier.

A lock-in amplifier's ability to handle large signals without overloading and losing data is known as dynamic reserve. For pulsed field experiments a lock-in with high dynamic reserve may be useful. The Stanford SR850 lock-in is one commonly used at NHMFL.

One way to stop overloading from dB/dT pick-up is to decrease the lock-in gain (sensitivity). Note that the dB/dt pick-up comes from an open-loop induced voltage independent of the instrumentation.