5-2 Signal Management
878695
Personal Daq User’s Manual
Data Acquisition Terms and Meanings
Differential mode
voltage
Differential mode voltage refers to a voltage difference between two signals
referenced to a common point.
Example:
Signal 1 is +5VDC referenced to
common. Signal 2 is +6VDC referenced to common. If the +5VDC is used as the
reference, then the differential voltage is (6 - 5), or +1VDC. If the +6VDC is used
as the reference, then the differential voltage is (5 - 6), or –1VDC. ).
The differential mode measures a voltage between 2 signal lines for a single
channel. (Also see
single-ended mode
).
ESD
Electrostatic discharge (ESD) is the transfer of an electrostatic charge between
bodies having different electrostatic potentials. This transfer occurs during direct
contact of the bodies, or when induced by an electrostatic field. ESD energy can
damage an integrated circuit (IC); so safe handling is required.
Excitation
Some transducers [e.g. strain gages, thermistors, and resistance temperature
detectors (RTDs)] require a known voltage or current. Typically, the variation of
this signal through the transducer corresponds to the condition measured.
Gain
The degree to which an input signal is amplified (or attenuated) to allow greater
accuracy and resolution. Gain can be expressed as ×n or ±dB.
Isolation
The arrangement or operation of a circuit so that signals from another circuit or
device do not affect the
isolated
circuit.
In reference to Personal Daq,
isolation
usually refers to a separation of the direct link
between the signal source and the analog-to-digital converter (ADC), as well as
the 500V isolation form the PC. Isolation is necessary when measuring high
common-mode voltage.
Linearization
Some transducers produce a voltage in linear proportion to the condition measured.
Other transducers (e.g., thermocouples) have a nonlinear response. To convert
nonlinear signals into accurate readings requires software to calibrate several
points in the range used and then interpolate values between these points.
Multiplexer (MUX)
A device that collects signals from several input channels and outputs them on a
single channel.
Sample (reading)
The value of a signal on a channel at an instant in time. When triggered, the ADC
reads the channel and converts the sampled value into a designated bit value.
Scan
The channels that are selected for sampling.
Single-ended mode The single-ended mode measures a voltage between a signal line and a common
reference that may be shared with other channels. (Also see
differential mode
).
Trigger
An event to start a scan or mark an instant during an acquisition. The event can be
defined in various ways; e.g., a TTL signal, a specified voltage level in a monitored
channel, a button manually or mechanically engaged, a software command, etc.
Some applications may use pre- and post-triggers to gather data around an instant
or based on signal counts.
TTL
Transistor-Transistor Logic (TTL) is a circuit in which a multiple-emitter transistor has
replaced the multiple diode cluster (of the diode-transistor logic circuit); typically
used to communicate logic signals at 5 V.
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