Measurement Computing DAC488 v.1 - Manual (Page 48)

42 DAC488 Calibration DAC488 User’s Manual
Manual Calibration Procedure
Part I: Connections & Preparations
1. Connect the DAC488 to the IEEE controller using an IEEE 488 cable.
2. Connect the negative input of the voltmeter to the Port 1 L (Low) output.
3. Connect the positive input of the voltmeter to the Port 1 H (High) output.
4. Set the IEEE bus address of the DAC488 to 9.
5. Turn the DAC488 on, and allow it to warm up for at least one hour before beginning the calibration
procedure.
Part II: Acquiring the Gain Calibration Constants
1. After the DAC488 has warmed up for at least one hour, initialize the DAC488 by sending an IEEE 488
Interface Clear ( IFC ). Command sent to the DAC488:
CLEAR 09
2. Select Port 1, Direct Control Mode, Autoranging disabled, select the +10 volt range, set the Offset to 0,
set the Positive and Negative Gain constants to 128, program the port to output 0 volts. Command sent
to the DAC488:
OUTPUT 09; P1 C0 A0 R3 H0 J128,128 V0 X
3. Measure and record the port 1 output voltage. Call this voltage ZVAL .
4. Program the DAC488 port 1 to output 10 volts. Command sent to the DAC488:
OUTPUT 09; V10 X
5. Measure and record the port 1 output voltage. Call this voltage PVAL .
6. Program the DAC488 port 1 to output -10 volts. Command sent to the DAC488:
OUTPUT 09; V-10 X
7. Measure and record the port 1 output voltage. Call this voltage NVAL .
8. Set the Positive and Negative Gain constants to maximum (255) and program the port to output 10
volts. Command sent to the DAC488:
OUTPUT 09; J255,255 V10 X
9. Measure and record the port 1 output voltage. Call this voltage MVAL .
10. Set the Positive and Negative Gain constants to minimum (0) and program the port to output 10 volts.
Command sent to the DAC488:
OUTPUT 09; J0,0 V10 X
11. Measure and record the port 1 output voltage. Call this voltage NOVAL .
12. The Gain Calibration Constants are computed using the following formulas:
•
Gain adjustment per bit = ( MVAL - NOVAL ) / 256
•
Pos. Error (in volts) = PVAL - ZVAL - 10
•
Pos. Gain Calibration Constant = (128 - Pos. Error) / Gain adjust per bit
•
Neg. Error (in volts) = NVAL - ZVAL - 10
•
Neg. Gain Calibration Constant = (128 + Neg. Error) / Gain adjust per bit
13. Once the Gain Calibration Constants have been computed, the positive and negative gains should be set
to these new values. This can be done using the Gain Calibration ( J ) command. For example, if the
positive and negative Gain Calibration Constants are 131 and 148 respectively, the command
J131,148 X should be sent to the DAC488.