Measurement Computing CIO-DAS48-PGA - Manual (Page 13)

13
Chapter 3
Functional Details
Single ended inputs
Single-ended inputs are two-wire connections between the signal source and the A/D board. A single wire
carries the signal, and is connected from the signal source to Channel n HI. The ground from the signal source
must be connected to LLGND (pins 49 or 50).
Differential inputs
Differential inputs are 3-wire analog hookups consisting of a signal high, signal low and chassis ground. The
signal source high is connected to Channel n HI, the signal source low is connected to Channel n LO, and the
signal source GND is connected to LLGND.
The benefits of differential inputs are the ability to reject noise which affects both signal high and low, and the
ability to compensate for ground loops or potentials between signal low and chassis ground.
Modified differential
Modified differential inputs for voltage measurements provide much of the environmental-noise immunity and
common mode rejection of fully differential inputs with the convenience of a two wire hookup.
Although differential inputs are often preferable to single-ended inputs, there are occasions when the floating
nature of a differential input can prevent making a valid reading. In those cases, the CIO-DAS48-PGA inputs
can be converted to modified differential.
Near the 50-pin connector on the board are positions for optional Single Inline Packages (SIP) of 10 K
resistors. Installing the SIP in RN7, RN8 and RN9 converts the analog inputs from fully differential to modified
differential with a 10 K reference to ground.
Notes : All three sips must be installed. It is not possible to mix channels.
After the SIPs are installed, signal connections require on Signal Source Hi be connected to Channel n HI and
signal source low be connected to Channel n LOW. No connection to LLGND is needed.
Special instructions and solder are packaged with the 10K SIP. Follow the installation instructions carefully and
use the solder provided. Use of other solder, or failure to follow instructions will probably result in a
degradation of the analog input's accuracy and will require out-of-warranty repair.
Current loop measurements
If you are configuring a CIO-DAS48-PGA for current measurements, do the following operations:
1. Remove (clip off) the SIPs from RN7, RN8, and RN9, if installed. These SIPs must not be installed if the
board is to be used for current measurement.
2. Install the resistor "CIO-DAS48-ISIP" kit. Install ISIPs in RN1, RN2, RN3, RN4, RN5, and RN6.
Special instructions and solder are packaged with the CIO-DAS48-ISIP kit. Follow the installation
instructions carefully and use the solder provided. Use of other solder, or failure to follow instructions will
probably result in a degradation of the analog input's accuracy and will require out-of-warranty repair.