Minimising Life Cycle Costs with Modern Consistency Transmitters

The basic design of common consistency transmitters, (rotary and blade type) has remained the same for over 40 years. Over that period only the electronics have been modernized, because of obsolete components and partly to  improve performance. Communication of the transmitters has developed and manufacturers have added several new digital communication protocols to enable the transmitter to communicate with the automation systems, like HART®, Fieldbus, FDT/DTM and AMS.

The drawbacks of the old designs are related to installation, maintenance and repairs. Old rotaries with massive structure require pipe expansions for less than 300mm (12") pipes. The motors are 3-phase motors and they need a high voltage supply with contactors and overload protectors. The drive belt wears and is a maintenance item. For a service check up, repair or cleaning of the sensing element, a user must wait as the line is drained before removing the
sensor.

In the new design of the rotary transmitter, by Kajaani Process Measurements Ltd, the squirrel cage motor is
replaced with a direct drive servo motor which is integrated with the drive shaft. This has resulted in a drastically smaller size, a 60 % decrease in weight, and the elimination of drive belt and the 3-phase high voltage in the sensor. Perhaps the most important feature of the new KC/5 rotary sensor is that it can be inserted in and removed from the process while the process is running.

Blade transmitters have had problems with seal failures because of the shear force transfer mechanism causing liquid leakage from the process into the sensor through the seals, causing total damage for the transmitter requiring expensive repairs or a unit exchange.

The new, seal-less design for blade transmitters prevents liquid leaks into the transmitter. The very strong and reliable process diaphragm does not have any hysteresis, offering excellent sensitivity and measurement accuracy. This strong diaphragm offers safe working conditions and enables users to replace electronic components without shutting down the process and without draining the line. The new KC/3 blade transmitter can be fully maintained and repaired onsite
without sending it to manufacturer for service.

This paper highlights safety, life-cycle costs, performance and maintenance features with the new designs and constructions used in modern consistency transmitters.