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

display	CH1			X
setting	output expand? offset?			(RCOSØ)
X	X+Xofst	yes	yes	X+Xofst
XOFST	Xofst	yes	yes	Xofst
R	R+Rofst	yes	yes	X+Xofst
R OFST	Rofst	yes	yes	X+Xofst
XNOISE	X noise	yes	yes	X+Xofst(enbw)
X5	X5	no	adjust	X+Xofst

The EXPAND and OFFSET conditions for each display are retained when the DISPLAY is changed. Thus, when the DISPLAY is changed from X to R, the EXPAND and OFFSET assume the conditions set the last time the DISPLAY was R. If the DISPLAY is changed back to X, the EXPAND and OFFSET return to conditions set for X.

R Output

The magnitude, R, is given by the equation:

R = {(X+Xofst)2 + (Y+Yofst)2}1/2 + Rofst

Note that the X and Y offsets affect the value of R while the X and Y expands do not.

The magnitude output has a resolution of 12 bits plus sign and is updated every 3.5 mS. To achieve maximum accuracy, the magnitude should be as large a fraction of full scale as possible.

R is expanded after the calculation. Thus, when R is expanded, the full scale resolution drops by a factor of 10 to about 9 bits.

Output Channel 1

The CHANNEL 1 output is available at the left hand OUTPUT BNC connector. The output parameter is selected by the DISPLAY setting and can be X, X OFST, R (magnitude), R OFST, X NOISE, or X5 (external D/A). (Note that X5 is the ratio output at power up. When displaying X5, the ratio output is 10R/X1). 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. (X5 may not be expanded). The output impedance is < 1Ω and the output current is limited to 20 mA.

The left hand analog meter always displays the CHANNEL 1 OUTPUT voltage. Accuracy is 2% of full scale.

The CHANNEL 1 LCD display provides a read-out of the displayed parameter in real units. The scale of the displayed quantity is indicated by the three scale LED's to the left of the display. This read- out auto ranges and will reflect the sensitivity added when the EXPAND function is on. When displaying X5, the scale LED's are off and the units are volts.

Rel Channel 1

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

When the DISPLAY is R or R OFST, the REL key sets the R OFFSET.

The REL key zeroes the X5 output when the DISPLAY is D/A.

Offset Channel 1

The OFFSET buttons control 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 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

11