Omega Engineering DAQ-12 - Manual (Page 10)

2. Circuit Board Description and Configuration
The base address of the DAQ-12 is selected using switches SW1 and SW2. The operating
mode of the DAQ-12 is controlled by jumpers J1 through J7, while DMA and interrupt
selections are set with jumpers J8 through J11. Connections to external equipment are made
through the high density 62-pin connector CN1.
2.1 Analog to Digital Converter
The analog to digital (A/D) section of the DAQ-12 accepts up to 8 differential or 16 single
ended inputs from the D-62 connector. These inputs pass through a multiplexer circuit which
selects the channel to be converted. The selected input is then amplified and presented to the
A/D converter to be digitized. The digital output of the A/D is latched into a buffer to be read
by the computer. The multiplexer circuit (MUX) selects one of the analog input channels to be
input to the A/D converter. The typical characteristics of the multiplexer circuit are:
Š switching time: 0.5 us
Š settling time: 3.0 us
Before operating the DAQ-12, the multiplexer circuit must be configured to accept either
differential or single-ended analog inputs. Single-ended mode measures the voltage
difference between the input signal and the analog ground reference of the DAQ-12 (e.g.
CH0+ and ground) while differential mode measures the voltage difference between two
input signals (e.g. CH0+ and CH0-).
Jumper J1 is used to configure the DAQ-12 for either single ended or differential inputs a
shown in Figure 2-1. Once configured, the input channel is software selectable through the
control word register.
5 6 7 8
1 2 3 4
5 6 7 8
1 2 3 4
J1
8 Differential Channels 16 Single Ended Channels
Figure 2-1. Jumper J1 Configuration
DAQ-12 Users Manual 10