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Data Acquisition 969597 Glossary G-1

Glossary

Acquisition

A collection of scans acquired at a specified rat

e as controlled by the sequencer.

Analog

A signal of varying voltage or current that communicates data.

Analog-to-Digital

Converter (ADC)

A circuit or device that converts analog values into digital values, such as binary bits, for use in

gital computer processing.

API

Application Program Interface. The interface program

within the data acquisition system’s

driver that includes function calls specific to the acquisition hardware and can be used with

user-written programs. Several languages are supported.

Bipolar

A range of analog signals with positive and negative values (e.g., -5 to +5 V); see uni

polar.

Buffer

Buffer refers t

o a circuit or device that allows a signal to pass through it, while providing

isolation, or another function, without altering the signal. Buffer usually refers to:

(a) A device or circuit that allows for the temporary storage of data during data transfers. Such

storage can compensate for differences in data flow rates. In a FIFO (First In - First Out)

buffer, the data that is stored first is also the first data to leave the buffer.

(b) A follower stage used to drive a number of gates without overloading the preceding stage.

impedance output (effectively, an impedance buffer).

Buffer Amplifier

An amplifier used primarily to match two different impedance points, and isolate one stage from

a succeeding stage in order to prevent an undesirable interaction between the two stages. (Also

see, Bu

ffer).

Channel

In reference to data acquisition, channel sim

ply refers to a single input, or output entity.

In a broader sense, an input channel is a sig

nal path between the transducer at the point of

measurement and the data acquisition system. A channel can go through various stages

(buffers, multiplexers, or signal conditioning amplifiers and filters). Input channels are

periodically sampled for readings.

An out

put channel from a device can be digital or analog. Outputs can vary in a programmed

way in response to an input channel signal.

Common mode

Common mode pertains to signals that are identical in amplitude and duration; also can be used

n reference to signal components.

Common mode

vol

tage

Common mode voltage refers to a voltage magni

tude (referenced to a common point) that is

shared by 2 or more signals. Example: referenced to common, Signal 1 is +5 VDC and Signal

2 is +6 VDC. The common mode voltage for the two signals is +5.5 VDC [(5 + 6)/2].

Crosstalk

An undesired transfer of signals between systems or system components. Crosstalk causes

signal interference, m

ore commonly referred to as noise.

Detection Signal

In relation to WBK17, a detection signal is one of 8 out

puts of the pattern detection module.

Each input channel has an associated detection signal (Detect 1 for Channel 1, Detect 2 for

Channel 2, etc.) A channel’s detection signal will go active high when that channel’s counter

value meets the setpoint criteria programmed into the pattern detection module. Detection

signals can be scanned along with any other channel in the scan group.

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