Measurement Computing WBK Options - Manual (Page 117)

The WBK18 module includes a built-in programmable voltage excitation source. This source can be used
to stimulate dynamic systems for transfer function measurements, and also serves as a test signal for the
input channels.
WBK18 Block Diagram
Current Source with Transducer Fault Detection
The WBK18 module provides constant current of 4mA to bias ICP transducers. The bias current is sourced through
the center conductor of the input channel BNC connector and returns to the WBK18 by the outer conductor. The
current source features an operating compliance of 24V and is short-circuit and overvoltage protected. Operating
compliance refers to the highest voltage that can be applied without change of the current source value. In the
absence of a transducer, the current source will output an open circuit voltage of 30V. For applications that do not
require bias, the current source can be disconnected from the input via software control on a per channel basis.
When the current source is enabled, the input voltage is continuously monitored with level detection circuitry.
Recognition of a voltage greater than 25V (transducer open) or less than 1V (transducer short) triggers a transducer
fault condition for the affected channel. This error is communicated to the user via a front panel LED and is also
available through a software status request at the end of an acquisition. When recognized, an error is latched until
the commencement of a new acquisition. Consequently, even intermittent faults are detected and communicated.
Detection of a fault does not, however, alter the acquisition process or its data.
Input Coupling
Each WBK18 channel offers the selection of three coupling modes: 0.1 Hz, 10 Hz, or DC. The 0.1 Hz path is a 1-
pole high-pass filter with a –3dB point at 0.1 Hz. The 10 Hz path is a 2-pole high-pass filter with a –3dB point at
10 Hz. The DC path provides a direct signal connection.
Programmable Gain Amplifier (PGA)
The WBK18 provides programmable gains of 1, 2, 5, 10, 20, 50, 100, and 200. These correspond to bipolar input
ranges of 5V, 2.5V, 1V, 500mV, 250mV, 100mV, 50mV, and 25mV. Additionally, there is a 25V DC-coupled only
range that is suitable for proximity sensor measurements. Range selection is programmable on a per channel basis.
WBK18, pg. 2 926896 WBK18, Dynamic Signal Input Module