Measurement-computing WaveBook rev.3.0 Manual de usuario descargar pdf (Pagina 173)

WaveBook User’s Manual,

6-21-99

B-1

Appendix B B

The following table defines data acquisition terms as used in this manual.

Data Acquisition Terms and Meanings

Acquisition A collection of scans acquired at a specified rate as controlled by the sequencer.

Analog signal A signal of varying voltage or current, resistance, temperature such as the output of a sensor.

Analog-to-Digital

Converter (ADC)

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

digital computer processing.

API Application Program Interface. The interface program within the WaveView system’s driver that

includes function calls specific to WaveBook hardware and can be used with user-written

programs (several languages supported).

Bipolar

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

Buffer

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

isolation, or another function, without materially 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).

(d) Buffer Amplifier (see Buffer Amplifier).

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, Buffer).

Channel

In reference to WaveBook, channel simply refers to a single input, or output entity.

In a broader sense, an input channel is a signal 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 output 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

voltage

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

used in reference to signal components.

Common mode voltage refers to a voltage magnitude (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 system components or channels. Crosstalk often

causes signal interference, more commonly referred to as noise.

Digital-to-Analog

Converter (DAC)

A circuit or device that converts digital values (binary bits), into analog signals.

DIP switch

A DIP switch is a group of miniature switches in a small Dual In-line Package (DIP).

Typically, they serve to provide application-specific hardware configuration or address setup for

a product.

Differential mode

voltage

The differential mode measures a voltage between 2 signal lines for a single channel. (Also

see single-ended mode).

Differential mode voltage refers to a voltage difference between two signals that are referenced

to a common point. Example: Signal 1 is +5 VDC referenced to common. Signal 2 is:

+6 VDC referenced to common.

If the +5 VDC signal is used as the reference, the differential mode voltage is:

+1 VDC (+ 6 VDC - +5 VDC = +1 VDC).

If the +6 VDC signal is used as the reference, the differential mode voltage is:

-1 VDC (+ 5 VDC - +6 VDC = -1 VDC).

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).

Excitation Some transducers [e.g. strain gages, thermistors, and resistance temperature detectors

(RTDs)] require a known voltage or current input in order for the sensor to operate. This

known input is called the Excitation.

Gain The degree to which a signal is amplified (or attenuated) to allow greater accuracy and

resolution; 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 Wavebook, isolation usually refers to a separation of the direct link between the

signal source and the analog-to-digital converter (ADC). Isolation is necessary when

measuring high common-mode voltage.

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