SRS Labs Lock-In Amplifier, SR530 manual Rsinø Output, Reference Input, Trigger Level

down, the offset advances in larger and larger increments, the largest increment being 10% of full scale. When the offset is turned OFF the applied offset returns to zero but the offset value is not lost. The next press of the upper offset key (return to ON) sets the offset to the previously entered value.

If an attempt is made to advance the offset value beyond full scale, the ON LED will blink. An offset up to 1.024 times the full-scale sensitivity may be entered. When the EXPAND is on, this is 10X the full scale output.

Note that the offsets (either manual offset or those generated by the REL function) represent a fraction of the full scale reading, and so their absolute value will change when the sensitivity scale is changed. A signal which has been nulled by an offset will not be nulled when the sensitivity scale is changed. The analog meter and the output BNC indicate the same value given by the equation:

Vout = 10Ae(AvVisinØ+V os) {if the output is Y}

where...
Ae	= 1 or 10 per the Expand
Av	=	1/Sensitivity
Vi	=	magnitude of the signal

Ø= phase between signal & reference Vos = offset (fraction of FS < 1.024)

When the DISPLAY is Y, Y OFST, or Y NOISE, the OFFSET keys adjust the Y OFFSET (which affects the Y (RSINØ) output). When the DISPLAY is Ø, the OFFSET keys do nothing. When the DISPLAY is X6, the OFFSET up and down keys set the output voltage of D/A output X6 (also on the rear panel) up to ±10.24V.

Expand Channel 2

The output EXPAND is toggled by pressing the key in the Channel 2 EXPAND section. The expand status is indicated by the X10, expand on, and the X1, expand off, LED's. Only the Channel 2 OUTPUT is affected, the Y (RSINØ) output is not expanded. Ø and X6 may not be expanded.

Y (RSINØ) Output

The analog output, Y+Yofst, is available at the Y (RSINØ) BNC connector. An input signal equal in magnitude to the selected sensitivity which is 90° out of phase with the reference oscillator will generate a 10V output. The output impedance is <1Ω and the output current is limited to 20 mA.

The Y (RSINØ) output is affected by the Y offset but may not be expanded. The Y (RSINØ) is not affected by the DISPLAY setting except for two cases. When the DISPLAY is set to Y OFST, the Y (RSINØ) output is the Y offset. When the DISPLAY is set to Y NOISE, the Y (RSINØ) output has a bandwidth equal to the ENBW (1 or 10 Hz) instead of the time constant.

Reference Input

The REFERENCE INPUT BNC is located in REFERENCE INPUT section. The input is ac coupled and the impedance is 1 MΩ . The dc voltage at this input should not exceed 100 V and the largest ac signal should be less than 10 V peak.

Trigger Level

The TRIGGER MODE indicator toggles from POSITIVE to SYMMETRIC to NEGATIVE when the TRIGGER MODE key is pressed.

If the center TRIGGER MODE LED is on, the mode is SYMMETRIC and the reference oscillator will lock to the positive zero crossings of the ac reference input. The ac signal must be symmetric (e.g. sine wave, square wave, etc.) and have a peak to peak amplitude greater than 100 mV. A signal with 1 Vrms amplitude is recommended. The phase accuracy of the reference channel is specified for a 1Vrms sinewave in the symmetric trigger mode.

If the upper TRIGGER MODE LED is on, the mode is POSITIVE. The trigger threshold is +1V and the reference oscillator will lock to the positive going transitions of the reference input. This mode triggers on the rising edges of a TTL type pulse train. The pulse width must be greater than 1 µ S.

If the lower TRIGGER MODE LED is on, the mode is NEGATIVE. The trigger threshold is -1V and the reference oscillator will lock to the negative

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