User manual

Input and Channel Configuration
Input Wiring 3
3-3
Shielded wires and sensors (such as thermocouples) should be used in environments
where "noisy" voltage sources are present. When shielded wiring is used, the shield is
normally connected to the L (low) input terminals for each channel. Alternate
configurations should be examined for each equipment application.
In situations where multiple inputs of different types are connected, a phenomenon
known as crosstalk can cause one signal to interfere with another and thereby introduce
measurement errors. The typical effect is an ac voltage channel can be interfered by
another high frequency/high voltage ac signal on the same Input Module.
3-Wire and 4-Wire Sense Input Configuration
For improved resistance measurement accuracy, the Product can connect to 3-wire (PRT
only) and 4-wire instruments with sense connections.
Sense connections cancel out the resistance of the test lead or wire that significantly
improves the accuracy of the measurement. As shown in Table 3-1, many thermistors,
platinum-resistance thermometers (PRTs) and resistors use a 3-wire or 4-wire sense
connection to eliminate lead wire resistance errors.
For 2-wire measurements, the wires can be connected to either the source or sense
channels ChX01 through ChX20. For 3-wire or 4-wire resistance measurements, the
source wires must be connected to channels ChX01 through ChX10 and the sense wires
to the set of terminals directly across from where the source is connected (channels
ChX11 through ChX20).
Note
The Product will not show or let the user select a 3-wire or 4-wire input on
channels ChX11 through ChX20.
Figure 3-2 shows an example of a 4-wire input (PRT) with sense wires connected to the
Input Module, then how it would look in the Channel Setup menu once it is properly
configured.
To use the sense connections, the channel connected to the source wires must be
configured as a 3-wire or 4-wire input as described in “Channel Configuration
Procedures” on page 3-7. When a channel is configured as a 3-wire or 4-wire input, the
Product automatically reserves the sense channel across from the source that prevents the
channel from being independently configured, as shown in Figure 3-2.