Differential Pressure Transducers
For Filter Condition Monitoring
Differential pressure transducers measure the difference in pressure between two points, typically referred to as P1 and P2 or high side and low side. A differential pressure transducer is a great choice for continuously monitoring the condition of a filter within a system. By using a differential pressure transducer, an operator has a live view, via the pressure transducers output signal, of the condition of the filter. This eliminates the need to repeatedly shut down the system for inspection. Using a differential pressure transducer is recommended over two individual pressure transducers because it eliminates potential compounded inaccuracies and the need to calculate the difference between two transducers.
A customer has a diesel generator and is looking to monitor the condition of the fuel filter. The line pressure of the application is 80 PSI and the customer would like to replace the filter when the downstream pressure reaches 50 PSI, a 30 PSI differential. We would recommend our CS14 Differential Pressure Transducer with a 4-20mA output signal and a calibrated differential range of 30 PSI.
When a new filter is installed and the generator is started, the pressure transducer will read 4mA (figure 1 below) as there is no differential between P1 and P2. As the filter removes contaminants and starts to become clogged, the output signal of the pressure transducer will increase because the downstream pressure is less than the upstream. In this application, the pressure transducers output signal will be 12mA when the downstream pressure falls to 65 PSI, a 15 PSI differential (figure 2 below). This will signify that half of the filter’s life is left. Eventually, as the filter continues to remove contaminants and become more clogged, the output signal of the transducer will reach 20mA (figure 3 below), signaling to the operator that 30 PSI of differential has been reached and it is time to change the filter.
A common question that comes up when working on filter monitoring applications is
“Can I just use two separate pressure transducers to measure the pressure differential?”
The answer is yes, two separate pressure transducers can be used to measure the differential pressure of a filter application. However, there are some potential issues that first need to be considered.
The first issue has to do with compounded inaccuracies. If you are using two pressure transducers, each with a ± 0.5% accuracy, your potential inaccuracy is doubled to ± 1%. If you were to instead use the CS14 Differential Pressure Transducer, you would only need to consider the accuracy of the single transducer, in this case ± 0.25% BFSL (± 0.5% for 2 PSI & below).
Also, while we temperature condition every sensor during the manufacturing process, it is possible for each transducer to behave differently in varying temperature conditions. For example, if the ambient temperature of the application goes from room temperature to 55°C, the upstream transducer could have a TC Span error of -0.5% while the downstream transducer has a TC Span error of +0.5%. Using a dedicated differential pressure transducer would eliminate this compounded inaccuracy potential.
The second issue is potential user error. When two single pressure transducers are used, customers will need to create a program or manually calculate the difference in readings from the upstream and downstream transducer. This introduces the potential for a mistake to be made which, if not caught early, could result in damage to equipment due to lack of flow in the system post filter or contamination of the system’s media due to a overly clogged filter. Our differential pressure transducers automatically calculate the difference in pressure from P1 to P2 and transmit a linear output signal to your PLC or control panel.