Measurement Computing WBK40 - Manual (Page 7)

Open Thermocouple Detection
The WBK40, WBK41, and DBK84 modules are equipped with open thermocouple detection for each
channel. This means that a broken thermocouple wire [or otherwise unconnected input] that is measured
will result in an off-scale reading. This is accomplished by applying a small bias current to each of the
channel inputs. Whenever a valid input is absent, the bias current saturates the input amplifier, resulting in
the off-scale reading. When in this “off-scale” state, however, the input amplifier draws more current from
the power supply. Specifically, the power draw of the module from
±15 V will increase by 0.75 mA for
each open channel.
If available power is limited, insert shorted TC plugs into unused channels. This will
minimize power consumption. Note that it is not enough to simply avoid scanning unused
channels; to minimize power consumption the channels must be physically shorted in the
hardware.
The power requirements, detailed in the product specification, assume worst case
connection conditions.
Digital I/O, Power, Counter/Timer, and DAC Connections (WBK41 Only)
The front panel of the WBK41 includes removable plug-in screw-terminal blocks for Digital I/O, Power,
Counter/Timer, and DAC (see following picture). Note that the DACs are only available if the DBK46
option is installed. Signal assignments are provided on page 2.
DIGITAL I/O (2 Terminal Blocks) POWER [Out] COUNTER - TMR D/A (DAC0, DAC1, DAC2, DAC3)
WBK41, Front Panel Connectors
CAUTION
Signal mix-up will result in erroneous readings and can damage equipment. Be sure to
connect signal lines to the proper screw-terminal connections.
Never move a wired terminal block from its intended terminal block socket to another.
The improperly routed signals, which result, can cause equipment damage.
Thermocouple & Multifunctional Modules 926896 WBK40 & WBK41, pg. 7