Omega Engineering OMB-DBK-34A, User Manual

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Signal Management 1
Signal Modes ...... 1-1
System Noise ...... 1-5
Using DBK Cards and Modules for Signal Conditioning ...... 1-6
Channel Control and Expansion ...... 1-7
Signal Acquisition ...... 1-9
Sequencer ...... 1-9
Scan Rate ...... 1-10
Triggering ...... 1-10
Counter/Timer Functions ...... 1-11
Simultaneous Sample and Hold (SSH) ...... 1-11
Two-Point Calibration of a Temperature Measurement System ...... 1-12
Overview ...... 1-12
An Example of Two-Point Calibration ...... 1-13
Calculation of Scale and Offset ...... 1-14
Implementing the Scale and Offset Constants in DaqView ...... 1-14
Converting Degrees from Celsius to Fahrenheit ...... 1-14
One Known Temperature Environment ...... 1-15
Use of a Temperature Calibrator ...... 1-15
CE Compliance ...... 1-15
CE Standards and Directives ...... 1-16
Safety Conditions ...... 1-16
Emissions/Immunity Conditions ...... 1-17
CE Enhancements for Existing Products ...... 1-17
Signal Modes
Input signals come in one of two modes, single-ended or differential . Expansion modules, LogBook, and
Daq device default setting use the single-ended mode. Some DBKs use differential inputs for certain kinds
of transducers; but DBK output is always single-ended. The following text briefly describes the two signal
modes.
Note: For DaqBook/100, /112, /120, jumper settings determine the signal mode. Single-ended is the
factory-set default. For DaqBoard and Daq PC-Card, choosing between differential and single-
ended inputs is made by software command.
Single-ended mode refers to a mode, or circuit set-up, in which a voltage is measured between 1 signal line
and common ground voltage (Vcm). The measured voltage may be shared with other channels. The
advantage of a single-ended
non-differential mode [over differential mode] is that it provides for a higher
channel count (16 vs 8 channels).
Differential-mode refers to a mode, or circuit set-up, in which a voltage is measured between 2 signal
lines. The resulting measured differential voltage is used for a single channel. Differential inputs reduce
signal errors and the induction of noise from ground current. The following illustration is an example of
how noise is reduced, or canceled-out, when using the differential mode.
In the schematic, voltage signal S
2
is subtracted from signal S
1
, resulting in the output signal shown. Noise
spikes with the same polarity, phase, and magnitude in each input signal cancel out—resulting in a clean
differential signal (S
1
- S
2
).
In the schematic, signals S
1
and S
2
are shown in-phase;
however, even if these signals were out of phase, the noise in
each (indicated by jagged lines) would still have the same
magnitude, phase, and polarity. For that reason, they would
still cancel out.
DBK Option Cards and Modules
886995
Signal Management 1-1