Measurement Computing DAC488 v.1 - Manual (Page 49)

DAC488 User’s Manual DAC488 Calibration 43
After setting the new gain values, the Offset Calibration Constant should be computed. (The Offset
Calibration Constant is affected by the Gain Calibration Constant.)
Part III: Acquiring the Offset Calibration Constant
1. After setting the new gain values, set the Offset of Port 1 to minimum (-255) and program Port 1 to
output 0 volts. Command sent to the DAC488:
OUTPUT 09; H-255 V0 X
2. Measure and record the port 1 output voltage. Call this voltage NOFFVAL .
3. Set the Offset of Port 1 to maximum (+255) and program Port 1 to output 0 volts. Command sent to
the DAC488:
OUTPUT 09; H255 V0 X
4. Measure and record the port 1 output voltage. Call this voltage POFFVAL .
5. Set the Offset of Port 1 to 0 and program Port 1 to output 0 volts. Command sent to the DAC488:
OUTPUT 09; H0 V0 X
6. Measure and record the port 1 output voltage. Call this voltage ZERR .
7. The Offset Calibration Constant is computed using the following formulas:
•
Offset adjustment per bit = ( POFFVAL - NOFFVAL ) / 512
•
Offset Calibration constant = Negative ZERR / Offset adjustment per bit
8. The Offset Calibration Constant should now be set to the newly computed value by using the Offset
Calibration ( H ) command. For example, if the Offset Calibration Constant is 18, the command H18 X
should be sent to the DAC488.
BASIC Calibration Program
The following BASIC program (filename DACCAL.BAS or CALIBR8.BAS ), which is included on disk, will
calibrate the DAC488 using a Personal488 IEEE 488 interface card, Driver488 software, and a Keithley
Instruments Model 196 DMM. Other DMMs (digital multimeters) may be used although the program will
need to be modified. All device dependent commands are contained in subroutines thus allowing these
commands to be easily changed to suit the DMM being used.
10 'DAC488 Calibration Program
20 KEY OFF
30 ' Requires a Keithley 196 DMM or equivalent
40 '
50 KAD$="26":DAD$="09"
60 DIM PFS!(4,3):DIM NFS!(4,3):DIM OFS!(4,3):REM error values
70 DIM GAIN(4,3,2):DIM OFFSET(4,3)
80 DIM RNG(3):RNG(1) = 1:RNG(2) = 5:RNG(3) = 10
90 'Establish communications with the IOtech Personal488
100 OPEN "\DEV\IEEEOUT" FOR OUTPUT AS #1
110 OPEN "\DEV\IEEEIN" FOR INPUT AS #2
120 'Reset the Personal488
130 IOCTL#1,"BREAK"
140 IOCTL#1,"RESET"
150 IOCTL#1,"FILL ERROR"
160 CLS
170 PRINT" DAC488 Calibration Program
180 PRINT
190 PRINT"Ensure DAC488 is connected to IEEE488 bus using address";DAD$
200 PRINT"Ensure 196 is connected to IEEE488 bus using address";KAD$
210 PRINT"Press any key to continue "
220 IF INKEY$="" THEN GOTO 220
230 '
240 'Initialize the DAC488 and the Keithley 196
250 '