Omega Engineering DAQ-12 User Manual

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n/a

0000 1111 1111 1111

0000 0111 1111 1111

0000 1000 0000 0000

0000 0100 0000 0000

2.5

0000 0000 0000 0000

1111 1100 0000 0000

n/a

-2.5

1111 1000 0000 0000

n/a

-5

Code

Bipolar

Unipolar

Voltage

Table 2-2. A/D Conversion Format Examples

NOTE: The 'voltage' column is the voltage applied to the A/D converter. This voltage is
equivalent to the input voltage multiplied by the amplifier gain.

2.2

Digital to Analog Converters

The digital to analog (D/A) section of the DAQ-12 consists of two independent 12-bit
multiplying D/A converters, and two independent two-stage output amplifiers. Digital data,
(output to the D/A converter by the CPU), is converted to an analog voltage by the D/A
converter, amplified by the output amplifiers and becomes output to the 62 pin connector at
CN1. The D/A converters used on the DAQ-12 are 12-bit resolution converters. Of the 16 bits
written to the D/A, only the 12 least significant bits (D0 - D11) are used for the conversion.
The 4 most significant bits (D12 - D15) are ignored.

The DAQ-12 implements multiplying D/A converters which makes the analog output
proportional to a reference voltage applied to the D/A. Under normal circumstances, the
reference voltage should be applied from the internal +5V reference source. An external
reference voltage may also be supplied to the D/A. This input from the D-62 connector should
not exceed 5 volts and has a typical input impedance of 7.5Kohms. The D/A reference voltage
source is selected using jumper J4 as illustrated in Figure 2-4.

4 5 6

1 2 3

D/A channel 0 reference

External Source

Internal Source

External Source

Internal Source

D/A channel 1 reference

Figure 2-4. Jumper J4 Configuration

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