SRS Labs Lock-In Amplifier, SR530 manual Dynamic Reserve, Status, Display Select, Channel 1 Display

Dynamic Reserve	Sensitivity Range
LOW	1 ∝ V through 500 mV
NORM	100 nV through 50 mV
HIGH	100 nV through 5 mV

Dynamic Reserve

The dynamic reserve (DR) is set using the keys in the DYNAMIC RESERVE section. The reserve is displayed by the three indicator LED's,HIGH, NORM, LOW. Only those dynamic reserve settings available for the sensitivity are allowed (see above table). For example, when the sensitivity is 500 mV, the DR will always be LOW.

The dynamic reserve and output stability of each setting are shown below.

Setting	Dynamic Reserve	Output Stability
		(ppm/°C)
LOW	20 dB	5
NORM	40 dB	50
HIGH	60 dB	500

Since a higher DR results in degraded output stability, you should use the lowest DR setting for which there is no overload indication. Note that using the Bandpass Filter provides about 20dB of additional DR and so allows you to operate with a lower DR setting.

Status

There are five STATUS LED's.

OVLD indicates a signal overload. This condition can occur when the signal is too large, the sensitivity is too high, the dynamic reserve is too low, the offset is on, the expand is on, the time constant is not large enough, or the ENBW is too large.

The OVLD LED blinks four times a second when an output is overloaded. This occurs if an output exceeds full scale. For example, during a quadrature measurement where X exceeds full scale while Y is near zero, a blinking OVLD indicates that it is safe to take data from the Y output since only the X output is overloaded. The signal path to the Y output is not overloaded. OVLD also blinks if a noise measurement is attempted on an output which exceeds full scale.

If the OVLD LED is on continuously or flashes randomly, then an overload has occurred before

the output, i.e. in the ac amplifier or output time constant. In this case, the dynamic reserve, sensitivity, time constant, or ENBW needs to be adjusted.

UNLK indicates that the reference oscillator is not phase locked to the external reference input. This can occur if the reference amplitude is too low, the frequency is out of range, or the trigger mode is incorrect for the reference signal waveform.

ERR flashes when an error occurs on one of the computer interfaces, such as an incorrect command, invalid parameter, etc.

ACT indicates activity on the computer interfaces. This LED blinks every time a character is received or transmitted by the SR530.

REM indicates that the unit is in the remote state and that the front panel controls are not operative. There are two remote states. The Remote-With- Lockout will not allow any inputs from the front panel. The Remote-Without-Lockout command allows you to return the front panel to operation by pressing the LOCAL key.

Display Select

The keys in the DISPLAY section select the parameters to be displayed on the OUTPUT METERS and the output of the two OUTPUT BNC connectors. The displayed parameters are indicated by one of the six DISPLAY LED's and can be either the two demodulator outputs (X Y), the demodulator output offsets (X OFST Y OFST), the magnitude and phase (R Ø), the magnitude offset and phase (R OFST Ø), the rms noise on X and Y (X NOISE Y NOISE), or the D/A outputs (X5 D/A X6). When displaying NOISE, the equivalent noise bandwidth is selected in the TIME CONSTANT section. When displaying D/A, the 2 outputs are the X5 and X6 rear panel D/A outputs, allowing the D/A outputs to be set from the front panel. This feature can be used to set the reference frequency when using the internal oscillator.

Channel 1 Display

The channel 1 outputs are summarized below. X is equal to RcosØ where Ø is the phase shift of the signal relative to the reference oscillator of the lock-in.

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