Stanford Research Systems DS345, Manual

Page: 92 / 139

Introduction
The calibration of the DS345 is composed of two parts: adjustment and cali-
bration. Adjustments are actual physical adjustments to variable resistors, in-
ductors, and capacitors to correct the DS345's oscillator, filters, and output
amplifier response. Calibration is the process of determining the calibration
constants ("calbytes") that the DS345 firmware uses to correct the output am-
plitude, etc.. The DS345's autocal procedure automatically determines the
most important of these calbytes.
The settings of the adjustments are, in general, very stable and should rarely
require change. If the adjustments are changed the corresponding calibra-
tions
must
be performed. However, the DS345 should need only routine
running of the autocal procedure and occasional complete recalibration to
maintain its performance.
Calibration Enable
The DS345 is shipped with calibration disabled. When calibration is disabled
only autocal is allowed, and direct access to the calbytes is prevented. The
internal calibration enable switch must be set to enable calibration. To set
the switch remove the DS345's top cover by removing its four retaining
screws (this will break the calibration seal). On units with an optional oscilla-
tor remove the mounting screw half way back on the left side of the chassis.
Next, remove the two left hand screws securing the top circuit board. This
board will hinge open (the optional oscillator hinges with the circuit board). In
the center of the bottom circuit board is a four position DIP switch labelled
SW300. Set SW300 switch 2 ON to enable calibration, and OFF to disable
calibration.
Calbytes
The DS345's calibration is controlled by calibration constants ("calbytes") that
the firmware uses to adjust the various output parameters. These calbytes
are stored in the DS345's RAM. Recalibration of the DS345 involves deter-
mining the values of the calbytes and storing the new values in RAM. The
calbyte values at the time of the DS345's production are also stored in ROM
and may be recalled at any time.
Direct access to the DS345's calbytes is allowed from both the front panel
and computer interfaces after calibration is enabled. From the front panel
press [SHIFT][CALIBRATE] three times to display the calbyte menu line.
There are two displayed parameters: on the left is the calbyte number, and
on the right is the calbyte value. The calbyte number and value may be mod-
ified with either the keypad or the MODIFY keys. To select an item use the
[SHIFT][RIGHT ARROW] and [SHIFT][LEFT ARROW] keys. The calbyte
number may be set between 0 and 509. The calbyte value may be set be-
tween -32768 and 32767. The complete set of factory calbyte values may be
recalled by pressing [CLR] any time a value is not being entered. The table
on the next page lists the DS345 calbytes. Shown is the calbyte number,
name, and meaning. The chart also indicates which calbytes are automati-
cally adjusted by autocal.
6-1
CALIBRATION