In some applications, a simple on/off switch just doesn't quite cut it. You'll find machinery that operates based on a variable input signal throughout various industries, particularly where a consistent pressure or temperature is required for optimal operation. These applications require a pressure sensor in a closed feedback loop to provide a signal to the Variable Frequency Drive (VFD) based on an output reading.
For the sake of this article, we'll be focusing on a VFD-powered pump system.
What is a Pressure Transducer?
In a variable-speed or constant-pressure pump system, a pressure transducer converts fluid pressure from the line into an electrical signal that is sent to the VFD powering the system. The VFD then uses this signal to increase or decrease the speed of the pump to match the pressure range required by the system. The main goal of the pressure transducer is to maintain a constant fluid pressure by acting as a signalling device to the VFD.
How a Pressure Transducer Works
The pressure transducer is connected to the output line of the system. An internal piston moves up and down based on the pressure in the line. The piston's movement changes the circuit resistance, sending a 4-20mA signal to the VFD. In turn, the VFD adjusts the speed of the pump to maintain a constant pressure.
When the pressure in the line goes up, the transducer amperage increases. The VFD receives this signal and decreases the frequency to lower the speed of the motor.
When the pressure in the line decreases, so too does the transducer amperage, sending a signal to the VFD to increase the frequency and speed up the motor.
The voltage across the pressure transducer is the power that runs the VFD in this closed-loop system.
Why Choose a Pressure Transducer?
Why are engineers choosing pressure transducers? Efficiency and reliability. Pressure transducers help to optimize pump speed, which drastically reduces the power consumed while in operation. In fact, systems with a pressure transducer are upwards of 30% more efficient than your traditional pump and switch set up.
Plus, with the reduced stress at start-up and shut down, the pump is running with significantly less strain on internal components, allowing for higher reliability and a longer life span.
How to Wire a Pressure Transducer
Wiring the pressure transducer is reasonably straightforward, as it is a two-wire setup. But first, you must understand how the components in the system work together; an analog output signal is required so that an input signal can be sent.
Source Power – Drive (VFD) – Motor/Pump – Output – Pressure Transducer – Drive (VFD)
Your typical 2-wire pressure transducer is simple to wire into the system. The pressure transducer's positive terminal (red wire) is to be connected to the positive terminal of the power supply. The green wire is to be connected to the power input of the VFD.
Here at eMotors Direct, we recommend you have a certified electrician complete the installation to avoid damaging your pressure transducer or any of the expensive equipment hooked up to the circuit.
Summary
Many industrial applications require consistent fluid pressure for equipment to operate correctly. A simple on/off switch doesn't have the capability to monitor the system's output and provide a signal to the controller. However, a pressure transducer can monitor the output line pressure and provide a signal to the VFD to maintain consistent pressure.
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