ÐаÑалог Weidmuller: Electronics - Analogue Signal Conditioning
ÐаÑалог Weidmuller: Electronics - Analogue Signal Conditioning
ÐаÑалог Weidmuller: Electronics - Analogue Signal Conditioning
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Glossary<br />
Technical appendix/Glossary<br />
Device categories<br />
Device groups<br />
DTM<br />
The device category determines which equipment can be used in which zone. There<br />
are six device categories. The categories 1 G, 2 G and 3 G are classifications for gas<br />
explosion protection (G = Gas). Equipment with 1 G is suitable for zones 0, 1 and<br />
2. Equipment with 2 G is suitable for zones 1 and 2. Equipment with 3 G is suitable<br />
for zone 2. The categories 1 D, 2 D and 3 D are classifications for dust explosion<br />
protection (D = Dust). Equipment with 1 D is suitable for zones 20, 21 and 22.<br />
Equipment with 2 D is suitable for zones 21 and 22. Equipment with 3 D is suitable<br />
for zone 22.<br />
Equipment is divided into groups I and II. Group I concerns underground<br />
mining while group II concerns explosion protection for gas and dust in all other<br />
applications.<br />
DTMs (Device Type Manager) are software drivers that are vendor- and deviceneutral.<br />
DTMs define functions for access to device parameters, troubleshooting,<br />
configuration and operation of devices The DTM specifies all device-specific<br />
information, functions and rules (such as the device structure, communication<br />
capabilities, internal dependencies and the human-machine interface (HMI)).<br />
Device manufacturers make available a Device Type Manager (DTM) software driver<br />
for each device or device group.<br />
E<br />
Earth loops<br />
A main cause of error in process systems comes from the earth loops. An earth loop<br />
occurs when two or more circuits are connected to each other and referenced to<br />
earth or a reference point. This reference point usually does not have the identical<br />
electrical potential at each position. When the two ends of the line are earthed at<br />
two different positions, the voltage differential between the two earth potentials on<br />
the line can lead to a compensating current that may corrupt analogue measurement<br />
signals. This occurs when field sensors have a separate earth or separate power<br />
feed. <strong>Analogue</strong> signal isolation amplifiers use electrical isolation to separate the input<br />
and output circuits thus preventing the measurement signal from being corrupted.<br />
Earth and ground loops<br />
Connection<br />
element without<br />
electrical isolation<br />
Connection<br />
element with<br />
electrical isolation<br />
W<br />
W.27
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