Perception Sensors and Instrumentation Perception Sensors and Instrumentation


Why Measure Flow?

The measurement of flow in a process increases the efficiency and safety of that process. Ultimately this has an affect on expenditure, as process efficiency and safety improve likewise plant running costs reduce.

Why Choose Differential Pressure Technique of Flow Measurement?

There are many flow measurement technologies available. Differential Pressure (DP), the most popular flow measurement technique, is the easiest and most comprehensive one.

DP techniques are easy to install, troubleshoot and calibrate. Alternate techniques are either very expensive or require specific dry, dust free environments .

DP is measured with a combination of a primary element which has to be in the duct to create a difference pressure and is connected to a secondary element, a transmitter, which records calculates and transmits the data to the control system.

Primary DP Elements

Venturi – Designed at the build stage of the plant, these ducts are big and can be difficult to set up.

Orifice Plate – A circular disc with holes inserted into the process duct can cause flow restriction which questions measurement reliability. Both venturi and orifice introduces restriction and hence pressure drop, which will at all time, add extra cost to operation of the fan.

Pitot Tubes – Inserted into the process duct at the desired place and time, DP is the difference in pressure measured at the front and back of the probe. Pitots have a wide operating process temperature range and have proven to be a very reliable method. Pitot tubes are the standard Primary element for accredited verification of flow profile

The Most Flexible DP Solution

The new PSI-2 FPU is a compact ALL in ONE flow monitor, fully assembled with fitted primary element. It provides three separate measurements in one simple, easy to use flexible solution in industrial applications. The static primary element component being either an S type or averaging pitot depending on application.

This fully assembled complete unit comprising of transmitter and integrated pitot tube reduces installation difficulties and costs whilst improving of accuracy. The pitot tube introduces a minimum of pressure drop in the duct – which can be ignored.

With installation via one simple insertion, it is able to acquire information from the process without disruption. Allowing correlation of flow data, which is calculated several times a second, with process changes enhancing process control.

Improved air/fuel ratios in combustion processors gives enhanced energy efficiency, reduced pollutant emissions and extended plant life.

Key Features

Key Applications


Static pressure input 0 to 207KPa absolute  
Operating differential pressure +/-1000Pa Approx 32m/s at STP [1]
Max. differential pressure 25KPa (250mbar) No damage
Max. differential pressure 50KPa Burst limit
Max. common mode pressure 207KPa Gauge all inputs Burst limit of differential pressure transducer
Repeatability (transducers) 0.1% FS [2]
Span drift differential & static pressure +/-0.25% FS [2]
Zero drift differential & static pressure +/-0.2% FS [2,3]
Ambient temperature range -20°C to 70°C  
Supply 8V to 30V 150mA maximum  
Process temperature range -20°C to 700°C Higher temperature ranges available on request
S-type style pitot tube 300mm to 2m  
Averaging style pitot tube 300mm to 2m  
Material available 316 stainless steel  
Temperature range -40°C to +700°C Higher temperature ranges available on request
Back purge Available for high dust applications  
Outputs Configurable analogue output assignable to any measured or calculated parameter
  Outputs are 4 – 20mA isolated
Serial interface RS485 MODBUS RTU selectable baud, parity, and stop bit
  HART All internal parameters are available via the RS485 and the USB communication
Connections IP69K 6-pole field connectors
  IP69K USB mini-B service connector
IP rating IP69K
[1] Specification based on standard differential transducer. Higher ranges are available but the burst common mode pressure remains at 207KPa gauge.
[2] As the velocity calculation is based on the square root of differential pressure, velocity errors are non liner. For low velocity accuracy the actual error must be calculated based on the transducer performance applied to the velocity calculation formula.
[3] The zero drift on the differential pressure is quoted with auto zero switched off. Improved zero performance can be obtained if the auto zero is enabled and configured for the application.