A crucial aspect of managing water resources involves ensuring the uninterrupted flow of water from reservoirs. An engineering consultancy was tasked with designing a system to monitor the head loss across a submerged water intake screen, located 400 metres from a control house at the bottom of a lake, approximately 10 metres deep. The primary purpose was to detect blockages of the 500mm pipe’s intake screen, which could occur due to icing or debris, to allow for preventative maintenance. A key challenge was the significant distance for signal transmission, with the customer expressing concerns about signal integrity over a 400-metre submerged cable run.
- Application: Head loss and blockage detection on a reservoir water intake screen.
- Challenge: Measuring a small differential pressure at a 10-metre depth.
- Constraint: A 400-metre cable distance between the sensors and the control station.
- Solution: Two submersible pressure transmitters with non-ventilated reference and 4-20mA output.
The application required measuring the pressure difference between the outside and inside of the water intake pipe. Under normal operation, this head loss would range from 4 to 60 centimetres of water column. However, if the screen became blocked, this differential pressure would increase significantly to around 4 metres of water column, providing a clear indication of a problem. The client, a civil engineer, had astutely identified a potential failure point with conventional solutions. They noted that a standard vented gauge pressure transmitter, which uses a vent tube to reference atmospheric pressure, would be impractical and unreliable over a 400 metre submerged length, citing the high risk of moisture ingress or tube blockage. This led them to seek a more robust solution using two independent, non-ventilated submersible sensors.
The proposed solution involved using two SLS-A series submersible pressure transmitters. One sensor would be mounted on the exterior of the pipe, potentially with a protective cover, to measure the static head pressure of the lake at that depth. The second sensor would be installed through the pipe wall to measure the internal pressure just behind the intake screen. The difference between these two readings would provide the critical head loss measurement.
The SLS-A series was ideally suited to overcome the specific challenges of this application. A key feature is the option for a 4-20mA amplified output, which is designed to transmit a stable and reliable signal over thousands of metres, easily addressing the 400 metre cable distance without signal degradation. Furthermore, the availability of a sealed gauge or absolute pressure reference was a direct answer to the customer’s concern about vented cables. A sealed reference design does not require a vent tube, completely eliminating the risk of moisture ingress on a long, underwater installation. By using two sensors with an identical pressure reference, any influence from atmospheric pressure changes is cancelled out when the differential is calculated, isolating the desired head loss measurement. The sensor’s construction, featuring a robust 316 stainless steel housing and an integrated, high-integrity molded PUR cable assembly, ensures its suitability for permanent and continuous submersion in a reservoir environment. This durable design provides a long operational life, minimizing the need for retrieval and maintenance from a 10 metre depth.
SLS-A Submersible Non-Vented Absolute Pressure Transmitter
- Level Range: 0 to 2.5 bar
- Range Type: Absolute, Non-Vented Reference
- Output Signal: 4-20mA (2-wire)
- Accuracy Class: 0.1%
- Cable Type: PUR
- Cable Length: 400
- Cable Length Units: Metres (m)
- Housing Material: 316 Stainless Steel
- Seal Material: Viton
- Diaphragm Material: 316 Stainless Steel
- Process Connection: G1/4 male DIN3852 with removable nose cone