DMM-16R-AT User Manual V1.31
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Page 32
10.
ANALOG OUTPUT CIRCUIT DESCRIPTION
10.1 Description
DMM-16R-AT uses a 4-channel 12-bit D/A converter (DAC) to provide 4 optional analog outputs. Model
DMM-16-NA-AT does not include the analog outputs.
A 12-bit DAC can generate output voltages with the precision of a 12-bit binary number. The maximum value
of a 12-bit binary number is 2
12
- 1, or 4095, so the full range of numerical values that you can write to the
analog outputs on Diamond-MM-16R-AT is 0 - 4095. The value 0 always corresponds to the lowest voltage in
the output range, and the value 4095 always corresponds to the highest voltage.
Note:
In this manual, the terms analog output, D/A, and DAC are all used interchangeably to mean the
same thing.
10.2 Analog Output Wiring
All analog output signals should use one of the analog ground pins on the I/O connector (Agnd) as their
common reference. Connecting the
– input of the analog signal to digital ground will induce significant noise in
the measurement and lower the measurement accuracy to approximately 8-10 bits. For lowest noise, use
shielded wiring when possible, keep the wiring as short as possible, and avoid running analog signals in
parallel with noisy power and digital signals or directly over noisy power and digital circuits. Sharing one Agnd
pin among several analog outputs is acceptable and will not degrade measurements.
10.3 Resolution
The
resolution
is the smallest possible change in output voltage. For a 12-bit DAC the resolution is 1/(2
12
), or
1/4096, of the full-scale output range. This smallest change results from an increase or decrease of 1 in the
D/A code, and so this change is referred to as 1 LSB, or 1 least significant bit. The value of this LSB is
calculated as follows:
1 LSB = Output voltage range / 4096
Example:
Output range = 0-5V;
Output voltage range = 5V
– 0V = 5V
1 LSB = 5V / 4096 = 1.22mV
Example:
Output range = 5V;
Output voltage range = 5V
– -5V = 10V
1 LSB = 10V / 4096 = 2.44mV
10.4 Output Range Selection
Jumper block J5 is used to select the D/A output range. Two selections need to be made.
First select whether you want fixed 5V or programmable D/A reference. For a fixed 5V reference install a
jumper in location 5, and for programmable install a jumper in P. Do not install a jumper in both 5 and P
simultaneously or unpredictable behavior will occur.
If you select programmable reference, the reference must then be programmed and calibrated using the
Universal Driver software. After the reference has been programmed and calibrated one time, it will be stored
in an EEPROM on the board and will be automatically recalled each time the board is powered up.
Next select bipolar or unipolar output. For bipolar output the outputs will swing between the selected
reference, and for unipolar output the output will swing from 0V to the selected reference. For bipolar output
install a jumper in the B position, and for unipolar output install a jumper in the U position. Again, do not install
a jumper in both B and U simultaneously or unpredictable behavior will occur.