Measurement Computing ZonicBook 618E rev.3.4 - Manual (Page 51)

Analog Common
The BNC shells for the analog input channels share common and are not isolated from earth ground. If a transducer
is effectively earth grounded through its connection to a device under test, there exists the possibility of added
measurement noise due to the ground loop that is created. This issue is minimized by electrically isolating the
transducer from the test device.
If the host computer is a desktop PC, then the computer ground will likely connect to the AC power line ground. If
the host computer is a notebook PC, then the computer ground could be: (a) floating, for example, when operating
on batteries, or (b) connected to a vehicle ground, for example, when using an automotive cigarette lighter adapter
in conjunction with the vehicle’s battery.
Additional measurement noise may be present when using earth grounded transducers.
For best results electrically isolate the input transducers from earth ground.
Current Source (ICP) with Transducer Fault Detection
If ICP is selected in software, a constant current of 4mA is supplied to bias ICP transducers. The bias current is
sourced through the center conductor of the input channel BNC connector and returns to the conditioning circuit 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 disabled 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. Faults are detected and communicated when
present. They are not latched. Detection of a fault does not alter the acquisition process or its data.
Input Coupling
Analog input channels 1 through 8 can be independently set in software to AC Coupling or to DC Coupling. When
AC Coupling is selected, the input signal will go through either a 0.1 Hz or 1 Hz high pass filter, as set in software.
When DC Coupling is selected the high-pass filter is bypassed.
Programmable Gain Amplifier (PGA)
The dynamic conditioning circuit 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 on a
per channel basis.
ZonicBook/618E 878595 Analog Signals 6-3