Performance Verification; Preliminary; Dc Offset - Stanford Research Systems SR446 Operation And Service Manual

3 Performance Verification

3.1 Preliminary

3.2 DC offset

SR446 400 MHz Programmable Gain Preamplifier
This chapter describes the equipment and procedures to verify the
SR446 is performing within specification.
Users may verify the amplifier offset (with respect to input) and/or the
AC gain accuracy (at 1 MHz). All equipment should be powered on
and warmed up for at least 2 hours prior to performing verification
measurements. The SR446 should be in a (23 ± 1)
environment, and the automatic offset calibration procedure (see § 1.3.1)
should be performed within 24 hours prior to verification.
Gather the following instruments and accessories:
1. Digital voltmeter, with better than 100 μV accuracy and resolution
(for amplifier offset verification)
2. Banana‑to‑BNC adaptor to connect BNC coax cable to voltmeter
3. SR865A 4 MHz DSP Lock‑in Amplifier (for AC gain verification)
4. Several 1 m (approximate) RG58 coax cables with BNC connectors
5. BNC Tee adaptor
6. BNC 50 Ω terminator
Input offset is measured at + 40 dB gain with the input grounded. It
is important to terminate the cable connection from the SR446 to the
voltmeter with a 50 Ω terminator to avoid possible amplifier oscillation.
The steps to verify the amplifier offset are:
1. Select input grounded by pressing the [Couple] button until
is illuminated.
2. Press the GAIN
40 dB (or 100 V/V).
3. Ensure the output filter is set to
FILTER button.
4. Connect a BNC coax cable to the + Out connector on the SR446
front panel.
button repeatedly until the display shows
by pressing the OUTPUT
full BW
21
∘
C ambient indoor
GND