As soon as LED number displays became available they were used to replace the moving coil readout to make a fairly practical dosemeter , rather than just a bleeper . But the LEDs pushed up the power consumption .

The really big step forward was the liquid crystal display which offered better readability in normal light , bigger numbers , and very low power consumption . One of the early ones , derived from the Bleeper III above , is still , very successfully , in production .

The advent of low-cost microprocessors meant dead time loss could be corrected . The first unit to do this was the Stephens Gammacom . At an early stage in development it failed at 15 mSv / h , but after some very minor changes , production units worked well up to 25 Sv / h . This meant the instrument could be used routinely at the µ Sv / h level , but was also suitable for extreme emergencies . 25 Sv / h corresponds to about 95 % dead time . These instruments are still popular on eBay .

These are very simple instruments without microprocessors , and do not have dead time correction , which means they under-read dose rates above 30 mSv / h .

( Acknowledgement to Vertec Scientific )

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