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Reference Materials > Converting Counts to Volts |
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Reference Materials > Converting Counts to Volts |
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In this help file, any time the term "2s complement, 16-bit binary value" is used, this value can be converted to volts using the methods described below. Data is returned from the instrument in the form of A/D converter counts (ADReading). These counts may be converted to volts for all instruments as follows (a simplified version of this formula is presented under the heading Simplified below):
where:
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.
Note that Vmax , Vmin , and gain factor vary by instrument. The following tables list each value of Vmax and Vmin by instrument and gain factor:
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Instrument |
Gain |
Unipolar Mode |
Bipolar Mode |
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Vmax |
Vmin |
Vmax |
Vmin |
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DI-1100, DI-145, DI-148, DI-1491, DI-150, DI-151, DI-154, DI-190, DI-194, DI-195, DI-11102, and DI-21082 |
1 |
N/A |
N/A |
+10 |
-10 |
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DI-4718B |
1 |
N/A |
N/A |
+5 |
-5 |
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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 |
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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 |
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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 |
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DI-11202 and DI-42082 |
1 2 5 10 20 50 |
N/A |
N/A |
100 50 20 10 5 2 |
-100 -50 -20 -10 -5 -2 |
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DI-41082 |
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 |
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DI-2108-P2 |
1 2 4 |
10 5 N/A |
0 0 N/A |
10 5 2.5 |
-10 -5 -2.5 |
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DI-158U & DI-715B |
1 2 4 8 |
N/A |
N/A |
+10 +5 +2.5 +1.25 |
-10 -5 -2.5 -1.25 |
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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 |
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DI-200, DI-2103 & DI-222 |
1 2 4 8 10 100 1000 |
10 5 2.5 1.25 1 0.1 0.01 |
0 0 0 0 0 0 0 |
+10 +5 +2.5 +1.25 +1 +0.1 +0.01 |
-10 -5 -2.5 -1.25 -1 -0.1 -0.01 |
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DI-201 & DI-220 |
1 2 4 8 10 100 1000 |
5 2.5 1.25 0.625 0.5 0.05 0.005 |
0 0 0 0 0 0 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 |
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DI-221TC |
1 10 100 1000 |
N/A |
N/A |
+5 +0.5 +0.05 +0.005 |
-5 -0.5 -0.05 -0.005 |
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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 |
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DI-401, DI-718B |
1 |
N/A |
N/A |
+5 |
-5 |
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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 |
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DI-720 |
1 2 4 8 |
N/A |
N/A |
+10 +5 +2.5 +1.25 |
-10 -5 -2.5 -1.25 |
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DI-730 and 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 |
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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 0 |
3 DI-210 and DI-410 instruments only support gains of 1, 2, 4, and 8.
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.
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Bipolar Mode |
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Instrument |
Gain |
Vmax |
Vmin |
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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, and 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 |
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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 |
Refer to the following examples:
Example 1: Say we are using a DI-200 board, configured for a gain of 1, operating in bipolar mode. From the chart, Vmax = +10V and Vmin = -10V. Plugging these values into the equation:
Example 2: Say we are using a DI-200 board, configured for a gain of 1, operating in unipolar mode. From the chart, Vmax = 10V and Vmin = 0V. Plugging these values into the equation:
Example 3: Say we are using a DI-200 board, configured for a gain of 2, operating in bipolar mode. From the chart, Vmax = +5V and Vmin = -5V. Plugging these values into the equation:
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.
The most simplified formula would be as follows:
so if your full scale range is +/-10Volts 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-2108-P, DI-4108, or DI-4208 (or other devices), do not use the last formula, which will degrade the precision from 16 to 14 bits.
