INFICON VGC403 Three-Channel Measurement and Control Unit - Manual (Page 46)

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tinb07e1-e 2011-07 Vacuum Gauge Controller
7.3 Calibration
7.3.1 Basics
The Vacuum Gauge Controller can only measure with
high accuracy when it is calibrated precisely. The Vac-
uum Gauge Controller is calibrated by INFICON before it
is shipped. Normally there is no need to change the cali-
bration data.
The calibration affects the A/D converters of the individ-
ual channels. The measuring curve of an ideal A/D con-
verter is a straight line which has a slope of one and runs
through the origin, i.e.:
• Factor = 1 (slope of the line)
• Offset = 0 (intersection with the y axis)
The curves of real A/D converters differ slightly from
these ideal values. Calibrating the unit means to deter-
mine the gain factors and the offset voltages of the indi-
vidual A/D converters and to store these calibration val-
ues.
The interface commands CAF and CAO are used to
access the calibration data of the unit.
7.3.2 CAO
Calibration offset. Calibration offset of the A/D converter.
The command is intended for service technicians of INF-
ICON only.
S: CAO[,±a.aaaaE±aa,±b.bbbbE±bb,±c.ccccE±cc]
<CR>[<LF>]
R: <ACK><CR><LF>
S: <ENQ>
R: ±a.aaaaE±aa,±b.bbbbE±bb,±c.ccccE±cc<CR><LF>
NOTE:
The CAO command can also be used with other pa-
rameters. See Chapter 7.3.4 Calibrating the unit,

46.
7.3.3 CAF
Calibration factor. Calibration factor of the A/D converter.
The command is intended for service technicians of INF-
ICON only.
S: CAF[,a.aaaaE±aa,b.bbbbE±bb,c.ccccE±cc]
<CR>[<LF>]
R: <ACK><CR><LF>
S: <ENQ>
R: a.aaaaE±aa,b.bbbbE±bb,c.ccccE±cc<CR><LF>
NOTE:
The CAF command can also be used with other pa-
rameters. See Chapter 7.3.4 Calibrating the unit,

46.
7.3.4 Calibrating the unit
The Vacuum Gauge Controller can be calibrated auto-
matically with the interface commands CAF and CAO.
The following auxiliary tools are required:
• D-Sub plug, 15-pin
• Soldering equipment
• High-precision voltage source for 10 volts
(10.000 V)
Calibration offset
1 Unplug the sensor of the respective channel
2 Connect pin 2 (Signal) and Pin 12 (Signal-GND) of
a 15-pin D-Sub plug with a wire strap. See
Chapter 3.3.4 SENSOR,  12.
3 Put the D-Sub plug with the wire strap onto the
sensor connection of the respective channel
• The input of the A/D converter is short-circuited
4 Use the serial interface to send the command
CAO,a to the unit. For the parameter a, use:
• 0 = Channel 1
• 1 = Channel 2
• 2 = Channel 3
CAUTION
Calibration.
If you input incorrect calibration data, the
Vacuum Gauge Controller cannot perform
accurate measurements anymore.
The interface commands for calibrating the
unit are intended for service technicians of
INFICON only.
Parameter Significance
±a.aaaaE±aa Calibration offset of channel 1
±b.bbbbE±bb Calibration offset of channel 2
±c.ccccE±cc Calibration offset of channel 3
Parameter Significance
a.aaaaE±aa Calibration factor of channel 1
b.bbbbE±bb Calibration factor of channel 2
c.ccccE±cc Calibration factor of channel 3