Reference Materials > Converting Counts to Volts

Examples

In this document, any time the term "2s complement, 16-bit binary value" is used, this value can be converted to volts. Data is returned from the instrument in the form of A/D converter counts. These counts may be converted to volts for all instruments.

ADReading is a signed integer value returned from the instrument. All bits after the LSB should be zero. Vmax is the maximum input voltage accepted at the selected gain. Vmin is the minimum input voltage accepted at the selected gain.

For complete accuracy, it may be necessary to turn ADReading into a 14-bit integer rather than a 16-bit integer. Vmax, Vmin, and gain factor vary by instrument.

Instrument Gain Unipolar Mode Bipolar Mode
Vmax Vmin Vmax Vmin
DI-1100, DI-11101,DI-145, DI-148, DI-1491, DI-154, DI-194, DI-195, DI-21082 1 N/A N/A +10 -10
DI-1551 1
2
4
5
8
10
16
20 		N/A N/A +50
+25
+12.5
+10
+6.25
+5
+3.125
+2.5 		-50
-25
-12.5
-10
-6.25
-5
-3.125
-2.5
DI-1120 and DI-4208 1
2
5
10
20
50		 N/A N/A +100
+50
+20
+10
+5
+2		 -100
-50
-20
-10
-5
-2
DI-4108 1
2
5
10
20
50		 N/A N/A +10
+5
+2
+1
+0.5
+0.2		 -10
-5
-2
-1
-0.5
-0.2
DI-245 and DI-2008 (voltage) 1
2
5
10
20
50
100
200
500
1000
2000
5000 		N/A N/A +50
+25
+10
+5
+2.5
+1
+0.5
+0.25
+0.1
+0.05
+0.025
+0.01 		-50
-25
-10
-5
-2.5
-1
-0.5
-0.25
-0.1
-0.05
-0.025
-0.01
DI-245 and DI-2008 (thermocouple) J
K
B
R/S
E
N
T 		N/A N/A 1200
1372
1820
1768
1000
1300
400 		-210
-200
250
-50
-200
-200
-200
DI-158U, DI-715B 1
2
4
8		 N/A N/A +10
+5
+2.5
+1.25		 -10
-5
-2.5
-1.25
DI-158UP 1
2
4
8
16
32
64
128
256
512		 N/A N/A +64
+32
+16
+8
+4
+2
+1
+0.5
+0.25
+0.125		 -64
-32
-16
-8
-4
-2
-1
-0.5
-0.25
-0.125
DI-2108-P2 1
2
4		 10
5
N/A		 0
0
N/A		 +10
+5
+2.5		 -10
-5
-2.5
DI-220 1
2
4
8
10
100
1000		 5
2.5
1.25
0.625
0.5
0.05
0.005		 0 +5
+2.5
+1.25
+0.625
+0.5
+0.05
+0.005		 -5
-2.5
-1.25
-0.625
-0.5
-0.05
-0.005
DI-221TC 1
10
100
1000		 N/A N/A +5
+0.5
+0.05
+0.005		 -5
-0.5
-0.05
-0.005
DI-222 1
2
4
8
10
100
1000		 10
5
2.5
1.25
1
0.1
0.01		 0 +10
+5
+2.5
+1.25
+1
+0.1
+0.01		 -10
-5
-2.5
-1.25
-1
-0.1
-0.01
DI-400, DI-410 1
2
4
8
10
100		 N/A N/A +10
+5
+2.5
+1.25
+1
+0.1		 -10
-5
-2.5
-1.25
-1
-0.1
DI-401, DI-718B, DI-4718B 1 N/A N/A +5 -5
DI-500, DI-5103 * * * * *
DI-700, DI-710 1
2
4
8
10
100
1000		 N/A N/A +10
+5
+2.5
+1.25
+1
+0.1
+0.01		 -10
-5
-2.5
-1.25
-1
-0.1
-0.01
DI-720 1
2
4
8		 N/A N/A +10
+5
+2.5
+1.25		 -10
-5
-2.5
-1.25
DI-730, DI-4730 1
10
100
1000
10000
100000		 N/A N/A +1000
+100
+10
+1
+0.1
+0.01		 -1000
-100
-10
-1
-0.1
-0.01
DI-50014 1
2
4
8		 N/A N/A +5 or +10
+2.5 or +5
+1.25 or +2.5
+0.625 or +1.25		 -5 or -10
-2.5 or -5
-1.25 or -2.5
-0.625 or -1.25

1 For Rate channel 9 please refer to the following table:

Gain Vmax Vmin
2
4
10
20
40
100
200
400
1000
2000
4000		 10000
5000
2000
1000
500
200
100
50
20
10
5		 0
0
0
0
0
0
0
0
0
0
0

2 For Rate channel 9 please refer to the following table:

Gain Vmax Vmin
2
5
10
20
50
100
200
500
1000
2000
5000
10000		 50000
20000
10000
5000
2000
1000
500
200
100
50
20
10		 0
0
0
0
0
0
0
0
0
0
0

3 Refer to the following table:

Instrument Gain Bipolar Mode
Vmax Vmix
All DI-500/510, DI-750/760, DI-718Bx, and DI-78x Series Instruments with signal conditioned inputs such as: DI-500-16; DI-750-16; DI-510-32; DI-760-32; DI-510-32 Expander, DI-718Bx, DI-785, DI-788; and Channels 1 through 16 on the DI-510-48 or DI-760-48 1
2
4
8		 +5
+2.5
+1.25
+0.625		 -5
-2.5
-1.25
0.625
All DI-500/510 and DI-750/760 Series Instruments with high level inputs such as: DI-500-32; DI-750-32; DI-500-32 Expander; DI-510-64; DI-760-64; DI-510-64 Expander; and Channels A1 through A32 on the DI-510-48 or DI-760-48 1
2
4
8		 +10
+5
+2.5
+1.25		 -10
-5
-2.5
-1.25

4 DI-5001 instruments have a jumper-selectable input range feature that allows them to be configured for either ±5 volts full scale or ±10 volts full scale.

Examples

Example 1: DI-158U at a gain of 1 (Vmax = +10; Vmin = -10).

Example 2: DI-220 in unipolar mode at a gain of 8 (Vmax = 0.625; Vmin = 0).

For DI-500 Series instruments, this equation converts the data returned into volts, just like any other instrument. If you have a DI-500 Series instrument with high level inputs (i.e., DI-500-32, DI-500-32 expander, DI-510-64, DI-510-64 expander, or channels A1 through A32 of the DI-510-48), this equation can be used to convert the returned data into volts. However, if you have a DI-500 Series instrument with signal conditioned inputs (i.e., DI-500-16, DI-510-32, DI-510-32 expander, or channels 1 through 16 of the DI-510-48), an additional calculation must be made to convert volts to whatever meaningful units the DI-5B module is measuring (Contact DATAQ Instruments support).

Simplified Formula

The most simplified formula would be:

If your full scale range is ±10 Volts the formula would read:

Usually this formula is good enough. But to be completely accurate we need to turn the ADReading into a 14-bit Integer. This can be done simply enough in VB and would make the formula look something like this:

or

where >>2 means to shift the data to the right 2 bits - turn it into a 14-bit integer.

For HiRes data from the DI-2008, DI-2108, DI-2108P, DI-4108, DI-4208 or other devices, don't use the last formula, which will degrade the precision from 16 to 14 bits.

 

 

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