Calibration; Adjusting The Cmrr; Adjusting The Gain - Stanford Research Systems SIM910 Operating Manual

3 – 2
3.1 Offset

3.2 Calibration

3.2.1 Adjusting the CMRR

3.2.2 Adjusting the gain

The SIM910 front-panel o set adjustment provides an easy way for
the user to null the amplifier's DC o set. The module should be run-
ning for at least 15 minutes before setting the o set. To do this, set
the input to GND. Set the gain to 100. Insert a small flat screwdriver
through the front-panel OFFSET hole and adjust the o set poten-
tiometer until the output of the amplifier is less than 1 mV. Return
to the desired input, A or A B. Note: the o set will be a ected by
CMRR adjustments. Thus the o set should be trimmed after any
CMRR adjustments.
In addition to the o set trimpot, there are 3 internal trimmers that
are calibrated at the factory. They are "CMRR Adjust" (R120), "Gain
Adjust" (R215), and "Freq Adjust" (C402). These are located on the
inside of the box and can easily be adjusted once the right side panel
of the SIM910 has been removed. Adjustments are most easily done
when the instrument is powered externally, or on the SIM900 Main-
frame remote cable. The module should be running for at least 15
minutes before doing any adjustments
The common mode adjustment minimizes the common mode re-
sponse of the amplifier by balancing the two sides of the front-end
JFET. Locate R120, the "CMRR Adjust" trimpot, on the inside of the
SIM910. Set the module's gain to 100, input mode to A B, coupling
to DC, and shield to grounded. Generate a 1 V amplitude sine wave
at 1 kHz. Carefully tee equal lengths of BNC cable to the module's
A and B inputs from the signal source. Adjust the "CMRR Adjust"
trimpot to minimize the output signal at 1 kHz; it should be below
5 mV.
The relative gains in the amplifier are set by 0.1% resistors; however,
the overall gain is adjusted with a "Gain Adjust" trimpot (R215).
Locate R215, the "Gain Adjust" trimpot, on the inside of the SIM910.
Set the module's gain to 100, input mode to A, coupling to DC, and
shield to grounded. Generate a
1 kHz, or a swept sine wave of the same amplitude. Connect the
signal source to the module A input. Measure the transfer function
of the module output relative to the signal input. Adjust the "Gain
Adjust" trimpot to make the transfer function equal 100 at 1 kHz.
Performance Tests
10 mV amplitude sine wave at
SIM910 JFET Preamp