Linearizing Function

Because of its construction, the PD 340 Flow Transmitter is, by its very nature linear, even without any electronic compensation.

However, in applications within the food and dairy industry it is common engineering practise not to use anything smaller than 25 mm as a pipe diameter, even for very low flow rates. Therefore, to further improve linearity, a special compensation function has been developed and implemented within the ‘Version 2’ electronics module (produced since January 1, 2005). Consequently, when this function is enabled, the PD 340 can now be used even at very low flow rates, but still offering the same well-known high accuracy measurement as normally experienced with higher flow rates.

During the flow calibration at the factory, the linearizing curve is calculated and downloaded to the electronic module. For this reason, all new PD 340 Flow Transmitters will hold the data needed by the linearizing function, when they are delivered as complete meters, i.e. meterhead and electronic module. If one of the new electronic modules needs to be mounted on a meter head with which it was not originally tested, and the linearizing function is to be used, data for the linearizing function can be downloaded to the electronic module using a PC with VIGO version 5.6 or higher installed (valid for extended version electronics only).

The graph below shows the linearizing curve for a specific flow transmitter. If this flow transmitter measures the flow rate at 20% of full scale, this value will be compensated by –0.01% of full scale.

Linearizing function

Enabling the linearizing function

The linearizing function can be enabled by setting Register E7, Dig. 5 to ‘1’.