Water vital role for sensor!

Here’s how it works: the draw wire sensor from Micro-Epsilon  measures the precise position of the control vane in the turbine. Using the measurement data from the sensor in combination with the water level in the millrace, the control actuator is adjusted to maintain system pressure, while maximising flow rate, which, in turn, produces the maximum electricity for the given amount of available water.

And here's how it works in practice: Ballywee Corn Mill in County Antrim, Northern Ireland, is a listed building, due to its Industrial Heritage, and features a recently restored and working 24-foot diameter waterwheel. Now a family home, the mill retains the grind stones and all the internal machinery required for the milling process.

Maximum efficiency

To exploit fully the water from the millrace, a water turbine has been installed. Modern water turbines represent a highly efficient means of producing renewable ‘green’ energy. The turbine control vane must be continually adjusted to maximise the available flow of water from the race. With its combination of high accuracy, resolution and long travel, the draw wire sensor from Micro Epsilon is utilised to provide feedback for the turbine control actuator, ensuring the turbine is always operating at maximum efficiency.

While the water turbine is completely separate from the waterwheel, they share the supply of water from the millrace. The water turbine includes an enclosed impeller which, via the belts, drives the generator mounted on top to produce electricity.

In control

The mill’s owner Des Wallace, who is also a technical specialist at Thales, installed the water turbine at the mill. He wanted to add his own controls to the water turbine, in order to optimise performance and efficiency. He explains: “Water from the millrace enters a 300mm diameter pipe and travels down to the turbine. Over the distance of the pipe, it falls ten metres, which is what produces the pressure to spin the turbine. Within the turbine is a control vane that must be adjusted to optimise efficiency. If the control vane is opened too much, the pipe will not backfill. 

“With the control vane closed too much, the pipe will produce pressure and backfill, but with a reduced flow rate. So, depending on the available amount of water in the river and millrace, the control vane has to be adjusted to maintain pressure, while maximising flow rate to produce the maximum electricity for the given amount of available water.”

Open-and-closed case

He continues: “The control vane is opened and closed by a linear actuator. The draw wire sensor measures the precise position of the control vane. An ultrasonic sensor measures the height of water in the millrace – which is proportional to flow rate. The control servo measures the height of the water in the millrace and opens or closes the control vane via the actuator to maximise flow rate, while ensuring the pipe remains full, producing maximum pressure.”

‘Sensorble’ solution

The draw wire sensor is a wireSENSOR WDS-1000-P60 from Micro-Epsilon. High quality precision internal components and a rugged design ensure high operational reliability and a long service life. This version of the sensor has a measuring range of 1,000mm, a potentiometer output (analogue voltage output) and a linearity of ± 0.1% F.S.O. Mounting grooves are provided on the four sides of the sensor’s aluminium housing, which enable simple, flexible mechanical mounting. 

Draw wire sensors from Micro-Epsilon are available in a range of compact housings, with both analogue and digital output types, and can measure distances up to 50,000mm.

“I approached Micro-Epsilon for a draw wire sensor,” adds Wallace, “as I had previous history with them from my work at Thales, where I made contact with Micro-Epsilon several years ago for a specific transducer requirement. For this project, I required a draw wire sensor with a long travel range that could also achieve good linearity and resolution. The sensor also needed to be rugged and able to operate consistently in a harsh environment.”