Pressure transmitters: It’s class that counts


Courtesy of KELLER AG für Druckmesstechnik

KELLER would like to do away with DIN standards. The company is backing the introduction of an accuracy class, as it did for pressure gauges. The conditions under which the class is complied with are described in specifications.

The new EC standards make it more difficult for companies to manufacture their own transmitter electronics. Changing from OEM transducers to OEM transmitters is recommended for the good of the customer.

Thirty years of Series 10 - a little history
In the 1970’s, companies in areas such as hydraulics and water management were being confronted with increasing customer demands for low-cost electronic pressure measuring instruments. Pressure sensors such as thin-film and piezoresistive sensors were in a price range that could not be supported by this emerging market, and many companies launched their own development projects in an attempt to develop a low-cost sensor. In the majority of cases the electronics were developed quickly, but pressure transducers were more problematic.

This gap was filled by KELLER Series 10 transducers from 1978 onwards. That which followed was the beginning of the triumphant march of piezoresistive technology through all usage areas. Well-known companies in the industry, some of whom have now had their own sensor technology for quite some time, did not wish to wait any longer for their own developments and flooded the markets with this new piezoresistive Series 10 transducer.

The range of OEM installation components has expanded considerably over the years. New technologies such as diaphragm high-temperature soldering and laser welding have introduced some significant improvements, making it possible to reduce the diameter to 9 mm without affecting the performance features.

Although OEM-transmitters (OEM-transducers with electronics) have been in the product range for years, the proportion thereof in relation to OEM transducers is only about 2%. The success of CIO (Chip in Oil) technology, where the amplifier is located adjacent to the sensor on the glass feed through in the oil chamber, has also been limited.

This probably has to do with the fact that companies wish to have as much of their own manufacturing depth as possible. Plus the fact that the high output signal of piezoresistive transducers makes it relatively simple to realize the amplifier electronics. The compensating and trimming resistors in the circuit are therefore soldered on just like they were 30 years ago; resistors that are becoming increasingly difficult to obtain because they are rarely used elsewhere.

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