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6. Adjustment of the semi-bridge converter for SE Ex sensing heads
The converter must be fitted into a powered Dräger RailGard-Wx for the adjustment
procedure. A Polytron SE Ex sensing head has to be connected with the converter.
1. Adjusting the supply voltage for the semi-bridge
• The semi-bridge current can be measured with a voltmeter at two test
points on the right hand side of the converter module.
• The converter is factory set to 270 mA, which is the required
sensor current for a Polytron SE Ex PR M, all other Pellistor based
systems need to be adjusted.
• The sensor current can be adjusted via the associated potentiometer The
following chart shows the voltages at the test point for various sensor
supply currents.
Converter supply
current in [mA]
Voltage at test point for
Converter current in [V]
Converter supply
current in [mA]
Voltage at test point for
Converter current in [V]
250 1,248 275 1,373
251 1,253 276 1,378
252 1,258 277 1,383
253 1,263 278 1,388
254 1,268 279 1,393
255 1,273 280 1,398
256 1,278 281 1,403
257 1,283 282 1,408
258 1,288 283 1,413
259 1,293 284 1,418
260 1,298 285 1,423
261 1,303 286 1,428
262 1,308 287 1,433
263 1,313 288 1,438
264 1,318 289 1,443
265 1,323 290 1,448
266 1,328 291 1,453
267 1,333 292 1,458
268 1,338 293 1,463
269 1,343 294 1,468
270 1,348 295 1,473
271 1,353 296 1,478
272 1,358 297 1,483
273 1,363 298 1,488
274 1,368 299 1,493
275 1,373 300 1,498
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