Каталог Weidmuller: Electronics - Analogue Signal Conditioning

Technical appendix/Glossary
Glossary
Overvoltage category
The overvoltage categories are described in DIN EN 60664-1. The category dedictes
the insulation clearance gaps required. Category III is the default specification
(EN 50178).
• Overvoltage category I
Devices that are intended to be connected to the permanent electrical building
installation. The measures for limiting transient surge voltages to the proper level
are taken outside of the device. The protective mechanisms can either be in the
permanent installation or between the permanent installation and the device.
• Overvoltage category II
Devices that are intended to be connected to the permanent electrical building
installation (such household appliances or portable tools).
• Overvoltage category III
Devices that are a part of the permanent installation and other devices where
a higher degree of availability is required. This includes the distributor panels,
power switches, distribution systems (including cable, busbars, distributor boxes,
switches and outlets) that are part of the permanent installation, devices intended
for industrial use, and devices that are continually connected to the permanent
installation (such as stationary motors).
• Overvoltage category IV
Devices that are intended to be used on or near the power feed in a building’s
electrical installation – ranging from the main distribution to the mains power
system. This includes electrical meters, surge protection switches and ripple
control equipment.
W
P
Passive isolator/ input loop powered
Passive sensor
Generates its power supply from the input signal (0/4–20 mA).
The amount of current needed internally is so small that the measurement signal is
not influenced. Transformers are used to provide the isolation between the input and
the output.
The advantages include: eliminates the influence of the mains power system, highly
accurate, minimal signal delay, and minimal power used. Passive isolators do not
function free from feedback;
so a load change on the output circuit will automatically effect the input circuit as
well.
Contains passive components whose parameters can be changed by the measured
variables. A primary electronic mechanism converts these parameters into electric
signals. An auxiliary external power source is needed for the passive sensor. Passive
sensors can be used to determine both static and semi-static measured variables.
For this reason, the majority of sensors have a passive construction. Examples of
this type include load cells and resistance thermometers.
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