Application Note

Glossary of terms
4-20 mA loop A process control circuit in which the devices communicate process variable signals
and control signals in a range from a low of 4 mA to a high of 20 mA. This corresponds
to the older pneumatic system, which ranged from 3 to 1
5 PSI.
Compliance voltage The voltage a current source develops when attempting to drive a mA signal through a
resistive load
.
DMM Digital multimeter. A meter that measures multiple electrical quantities, such as voltage,
current, and resistanc
e.
Electronic valve positioners A device that controls the position of a valve, based on an analog or digital electrical
input
. Many applications use, alternatively, pneumatic valve positioners to control valve
position-based on a pneumatic input signal (3 to 15 PSI).
A
TEX/Ex
A
Tmospheric EXplosibles (French for explosive atmospheres) rating.
The European ATEX directive (94/9/EC) applies to all industrial equipment which will
or may be used in an explosive atmosphere. Regulations state that measures must be
taken to protect personnel, plant and the environment by ensuring that potentially
explosive atmospheres cannot be ignited.
FM approval Factory Mutual (FM) is a regulatory agency that provides third party product certification
for intrinsically safe equipment used in the United States. FM verifies electrical equip-
ment compliance based on accepted standards from FM, the American National
Standards Institute (ANSI), and the International Electrotechnical Commission (IEC).
Ground loop An undesirable circuit that develops because individual grounding points or paths are
tied to different earth potentials instead of to the common grounding or bonding points
(e.g., the main bonding jumper). This results in a difference of potential (voltage)
between the grounds and allows current to flow between them via the process loop.
Linearity The closeness of a calibration curve to a specified straight line. Linearity is expressed as
the maximum deviation of any calibration point from a specified straight line.
Intrinsically safe An apparatus containing circuits in which any spark or thermal effect is incapable of
causing ignition of a mixture of flammable or combustible material in air under pre-
scribed test conditions.
Loop-powered isolator A device that produces an electrically isolated mirror image of the input side 4-20 mA
current.
mA Milliamp; a unit of electric current equal to one thousandth of an ampere.
Precision current shunt A conductor joining two points in a circuit to form a parallel circuit, through which a
precision voltage can be measured or derived.
RTD A temperature measurement sensor whose resistance corresponds to a specific temper-
ature. This device will change its resistance in response to a change in temperature.
Signal conditioner A circuit to modulate a signal so as to make it intelligible to, or compatible with,
another device, including such manipulation as pulse shaping, pulse clipping, compen-
sating, digitizing, and linearizing. The input side of a signal conditioner might be the
output of a sensor-in fractions of a mV-while the output side of the signal conditioner is
4-20 mA.
Strain gauge A measuring element for converting force,
pressure, tension, etc., into an electrical
signal.
Thermocouple A junction of dissimilar metals that generates
a small voltage correlated to the temperature
of the junction.
µA or uA Microamp; a unit of electric current equal to
one millionth of an ampere.
Vernier A small, movable, graduated scale running
parallel to the fixed graduated scale and used for
measuring a fractional part of one of the divisions of
the fixed scale.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The N
etherlands
For more information call:
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ax (425) 446-5
1
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6
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ax (3
1 40) 2 675 222
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00)-36-
F
LU
KE or
Fax [phone]
Other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com
©2004 Fluke Corporation
. All rights reser
ved
.
Trademarks are the property of their respective owners.
Printed in U.S.A. 7/2004 1627722 A-US-N Rev C
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