MKS 651D Series, User Manual, Page: 140 / 162

Troubleshooting Chapter Seven: Maintenance and Troubleshooting
128
How To Calibrate the Span of the A/D Converter
The controller’s A/D (analog-to-digital) converter converts the analog input to a digital value that
the controller uses. The span of the A/D converter is calibrated at the factory. However, you
may need to recalibrate the span if your unit issues a checksum error when you power up the
controller, or if the transducer’s readings are incorrect.
How To Calibrate the Span of the A/D Converter using Local Control
To calibrate the span of the A/D converter:
1. Apply a known voltage of b6.6 Volts and +7.4 Volts to the pressure input pins 2
and 12 on the Transducer connector. (connect pin 12 to pin 5)
Refer to Table 9, page 22, for the Transducer connector pinout.
2. Press the [ ] and [S
TOP
] keys simultaneously for about three seconds.
The screen displays:
CAUTION
CALIBRATION MODE
3. Press the [S
ET
P
OINT
C] [S
ET
P
OINT
A] and [S
ET
P
OINT
E] keys, in this order .
The screen displays:
CAL VOLTS:
REF COUNTS:
Enter the known voltage value from step 1 as the Cal Volts.
4. Press the [S
TOP
] key to exit the calibration procedure.
The controller takes the Cal Volts value and assigns it to the converter reading of the
pressure, as an analog input. Calibrating the span of the A/D converter may take up to
5 seconds.