SRS Labs SR530, Lock-In Amplifier manual Auto Phase, Output Channel, Rel Channel, Offset Channel

possible. If R is less than 0.5% of full scale, the phase output defaults to zero degrees.

The Phase Output may not be expanded and the OFFSET keys do not offset the Phase Output. However, the Phase Output can be offset using the Reference Phase shift.

The Reference Phase shift, which may be adjusted via the phase controls in the reference section, rotates the lock-in's internal coordinate axes relative to the reference input. The Phase Output is the phase difference between the signal and the lock-in's coordinate system. For example, if a signal exactly in phase with the reference input is being measured and the Reference Phase shift is zero, the Phase Output will be zero also. This is because the lock-in coordinate system is in phase with the reference input and signal. If the Reference Phase shift is set to +45 degrees, then the lock-in coordinate system rotates to +45 degrees from the reference input. Thus, the reference input is now at -45 degrees from the lock-in coordinate axes. Since the reference and signal are in phase, the signal is now at -45 degrees with respect to the lock-in coordinates and the Phase Output will be -45 degrees.

The sum of the Reference Phase shift and the Phase Output is the absolute phase difference between the signal and the reference input.

Therefore, the Phase Output may be offset to zero by adjusting the Reference Phase shift. This is sometimes necessary when the Phase Output is near 180 degrees and varies between +180 and - 180 degrees.

Output Channel 2

The CHANNEL 2 output is available at the right hand OUTPUT BNC connector. The output parameter is selected by the DISPLAY setting and can be Y, Y OFST, Ø (phase), Ø (phase), Y NOISE, or X6 (ext D/A). All outputs are ±10V full scale when the EXPAND is off. With the EXPAND on, the output is multipled by 10, effectively increasing the full scale sensitivity by 10. (Ø and X6 may not be expanded). The Ø (phase) output is 50 mV/deg (20 deg per Volt) up to ±9 V (±180 deg). The output impedance is <1Ω and the output current is limited to 20 mA.

The right hand analog meter always displays the CHANNEL 2 OUTPUT voltage. Accuracy is 2% of full scale.

The CHANNEL 2 LCD display provides a read-out of the displayed parameter in real units. The scale of the displayed quantity is indicated by the four scale LED's to the right of the display. This read- out auto ranges and will reflect the sensitivity added when the EXPAND function is on. When displaying X6, the scale LED's are off and the units are volts.

Rel Channel 2

Every time the REL key is pressed, the displayed parameter is offset to zero. This is done by loading the displayed parameter's offset with minus one times the present output. If the output is greater than 1.024 times full scale, the REL function will not be able to zero the output. In this case, the OFFSET ON LED will blink and the offset value will be set to its maximum value.

The REL function and the manual OFFSET are both ways to enter the offset value. After using the REL key, the offset may be adjusted using the manual OFFSET.

When the DISPLAY is Y, Y OFST, or Y NOISE, the REL key sets the Y OFFSET (which affects the Y (RSINØ) output). If Y NOISE is being displayed, the REL function zeroes Y and the noise output will require a few seconds to settle again.

The REL key zeroes the X6 output when the DISPLAY is D/A.

Auto Phase

When the DISPLAY is Ø (phase), the REL key sets the Reference Phase Shift to the absolute phase difference between the signal and the reference. This is done by setting the Reference Phase Shift to the sum of the Reference Phase Shift and the present Phase Output. After auto- phase is performed, the Ø output will be 0 deg, R will be unchanged, X will be maximized, and Y will be minimized.

Offset Channel 2

The OFFSET section controls the manual offset. The offset is turned ON and OFF using the upper key in the OFFSET section. When the offset is ON, the lower two keys are used to set the amount of offset. A single key press will advance the offset by 0.025% of full scale. If the key is held

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