Ex-i Relays and Opto-Couplers
Often Times electronic equipment is required to carry out certain functions in potentially explosive atmospheres. To prevent potential ignition via a spark or arc in these environments, all components must be selected very carefully. Components meeting these requirements are generally referred to as intrinsically safe. This components must be tested such that they will not become an ignition point when subject to short circuits or adjacent component failures. They must also switch to a defined state when subjected to overload conditions.
Components acting as interfaces in the above-defined application must meet the highest criteria of strict insulation values and galvanic separation between interconnecting electrical circuits.
Intrinsically safe Reed Relays are generally used for applications with low switching frequencies. Standards for these components are presented in EN500200. Here the required air and creepage paths as well as the electric strength are defined in detail.
For voltage specification, a peak voltage of 375 Volts must not be exceeded in order to meet accepted worldwide standards. The sum of the input and output voltages must not be higher than 375 Volts Peak.
- The coil input has a voltage of 24 Volts max. and the contacts produce 230 VRMS or 325 volts peak output. Input plus output = 24 + 325 = 349 Volts peak. Here the safety margin for the voltage for the input and output meet their peak voltage limit of 375 volts.
- The air path for isolation of this voltage is 6mm and the creepage path is 10mm.The isolation inside the component through potting compounds is 2mm.
- Another important value is the Comparative Tracking index (CTI) value of plastic. In this case, the value must be greater than 175.
- The electric strength between the input and output is tested at 1500 VRMS or 2x the nominal voltage +1000
The certification was issued according to ATEX 94/4 EG by a German authority, the PTB. The MEDER relays and opto- couplers passed the tests successfully and received the following approval codes:
MRX-Relays: PTB 01 ATEX 2050 U
Opto-Coupler: 522, 542: PTB 01 ATEX 2043 U
525, 535: PTB 01 ATEX 2049 U
567: PTB 01 ATEX 2042 U
Generally, intrinsically safe approved components find application in the mining industry, chemical processing plants, refineries, power stations and high dust producing plants. Any potentially flammable atmospheres represent areas of applications for these products.
Our MRX series Reed Relays and our 525-03-0-1, 525-04-1,and 567-70-1-I Opto-coupler series are all ideal for this environment.
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