Max V
Min V
Single-Ended
2.44
0
Differential
2.44
-2.44
Special 0-3.6
3.6
0
Table 2.6.2-1. Nominal Analog Input Voltage Ranges for Low-Voltage Channels
Max V
Min V
Single-Ended
10.3
-10.3
Differential
N/A
N/A
Special -10/+20
20.1
-10.3
Table 2.6.2-2. Nominal Analog Input Voltage Ranges for High-Voltage Channels
U3 Calibration Formulas (Analog In)
The readings returned by the analog inputs are raw binary values (low level functions). An approximate voltage conversion can be
performed as:
Volts(uncalibrated) = (Bits/65536)*Span (Single-Ended)
Volts(uncalibrated) = (Bits/65536)*Span – Span/2 (Differential)
Where span is the maximum voltage minus the minimum voltage from the table above. For a proper voltage conversion, though,
use the calibration values (Slope and Offset) stored in the internal flash on the Control processor.
Volts = (Slope * Bits) + Offset
U3 Calibration Formulas (Analog Out)
Writing to the U3's DAC require that the desired voltage be converted into a binary value. To convert the desired voltage to binary
select the Slope and Offset calibration constants for the DAC being used and plug into the following formula.
Bits = (DesiredVolts * Slope) + Offset
U3 Calibration Formulas (Internal Temp)
Internal Temperature can be obtained by reading channel 30 and using the following formula.
Temp (K) = Bits * TemperatureSlope
U3 Calibration Constants
Below are the various calibration values are stored in the Mem area. Generally when communication is initiated with the U3, eight
calls will be made to the ReadMem function to retrieve the first 8 blocks of memory. This information can then be used to convert all
analog input readings to voltages. Again, the high level Windows DLL (LabJackUD) does this automatically.
Starting
Block #
Byte
Nominal Value
0
0
LV AIN SE Slope
3.7231E-05 volts/bit
0
8
LV AIN SE Offset
0.0000E+00 volts
0
16
LV AIN Diff Slope
7.4463E-05 volts/bit
0
24
LV AIN Diff Offset
-2.4400E+00 volts
1
0
DAC0 Slope
5.1717E_01 bits/volt
1
8
DAC0 Offset
0.0000E+00 bits
1
16
DAC1 Slope
5.1717E+1 bits/volt
1
24
DAC1 Offset
0.0000E+00 bits
2
0
Temp Slope
1.3021E-02 degK/bit
2
8
Vref @Cal
2.4400E+00 volts
2
16
Reserved
- -
2
24
Reserved
- -
Table 5.4-1. Normal Calibration Constant Memory Locations
Starting
Block #
Byte
Nominal Value
3
0
HV AIN0 Slope
3.1400E-4 volts/bit
3
8
HV AIN1 Slope
3.1400E-4 volts/bit
3
16
HV AIN2 Slope
3.1400E-4 volts/bit
3
24
HV AIN3 Slope
3.1400E-4 volts/bit
4
0
HV AIN0 Offset
-10.3 volts
4
8
HV AIN1 Offset
-10.3 volts
4
16
HV AIN2 Offset
-10.3 volts
4
24
HV AIN3 Offset
-10.3 volts
Table 5.4-2. Additional High-Voltage Calibration Constant Memory Locations
Format of the Calibration Constants
Each value is stored in 64-bit fixed point format (signed 32.32 little endian, 2's complement). Following are some examples of
fixed point arrays and the associated floating point double values.
Fixed Point Byte Array
{LSB, ..., MSB}
Floating Point Double
{0,0,0,0,0,0,0,0}
0.0000000000
{0,0,0,0,1,0,0,0}
1.0000000000
{0,0,0,0,255,255,255,255}
-1.0000000000
{51,51,51,51,0,0,0,0}
0.2000000000
{205,204,204,204,255,255,255,255}
-0.2000000000
{73,20,5,0,0,0,0,0}
0.0000775030
{255,122,20,110,2,0,0,0}
2.4300000000
{102,102,102,38,42,1,0,0}
298.1500000000
Table 5.4-3. Fixed Point Conversion Examples
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