An engineering consultancy required a robust and precise method for monitoring the water level in a shallow surface water stream. The application demanded a solution that could not only endure continuous submersion and varying environmental conditions but also provide consistently accurate hydrostatic level readings. The primary technical challenges involved compensating for atmospheric pressure changes and ensuring the long-term integrity of the sensor’s cable termination in an outdoor setting. The implemented solution utilized a submersible hydrostatic level transmitter paired with a specialized terminal junction box equipped with an atmospheric vent filter and optional surge protection.
- Application: Continuous level monitoring in a shallow surface water stream.
- Challenge 1: Achieving accurate hydrostatic depth measurement, which requires real-time compensation for barometric pressure changes.
- Challenge 2: Protecting the sensor’s sensitive atmospheric reference vent from moisture and particulate ingress at the termination point.
- Solution: An LMP307 series submersible level transmitter was combined with a KL1 series cable junction box.
An environmental engineering and consulting firm was tasked with a project to monitor the water level in a shallow surface water stream. This required a level sensing instrument that could be permanently installed in the stream to provide continuous and reliable data. The initial project scope had considered a measurement range that was determined to be too great for the shallow nature of the stream. After consultation, a more suitable requirement for a range between 3 to 6 metres of water depth was identified, necessitating a measurement solution that could be precisely configured for these lower-range applications.
The product solution centred around the LMP307 series submersible level transmitter. Its all-stainless steel construction, featuring a 1.4404 (316L) grade housing and a highly resilient 1.4435 (316L) grade diaphragm, provides excellent durability for long-term immersion in surface water, which can have varying levels of light pollution and chemical composition. A particularly important feature for this type of installation is the sensor’s removable protective cap. In a stream environment, the sensor is susceptible to being covered by silt, leaves, and other floating debris. This cap shields the sensor’s diaphragm from direct impact and fouling, and its simple, detachable design allows for easy removal for periodic cleaning in the field, ensuring that measurement accuracy is maintained without significant downtime.
A critical technical aspect of achieving accurate hydrostatic level measurement is the need to compensate for fluctuations in local atmospheric pressure. Without compensation, a change in barometric pressure would be incorrectly registered as a change in water level. The LMP307 series addresses this by incorporating a fine-bore ventilation tube within the shielded electrical cable. This tube allows the ambient air pressure at the surface to be transmitted down to the rear of the sensing diaphragm. This design effectively references the sensor to the local atmospheric pressure, ensuring that the output signal corresponds only to the true hydrostatic pressure, or depth, of the water.
While the integrated vent tube is essential for accuracy, its termination presents a significant challenge. The tube must be able to “breathe” ambient air, but it must also be protected from the ingress of moisture, humidity, and dirt, any of which could block the tube and cause pressure-locking, leading to significant measurement errors and potential sensor failure. The KL1 series terminal box was selected to provide a professional and protected termination point. This robust, aluminium die-cast enclosure is rated to IP66 ingress protection , making it ideal for a damp streamside environment. Its key feature is an integrated pressure compensation element fitted with a PTFE filter. This specialised filter allows air to pass freely into the sensor’s vent tube while effectively blocking the passage of water molecules and fine dust, ensuring the reference path remains clear and the sensor’s readings remain accurate over the long term.
For added system reliability in an outdoor installation exposed to the elements, the KL1 junction box was specified with an optional overvoltage protection module. Instrumentation installed in open areas is vulnerable to transient voltage spikes caused by nearby lightning strikes or power grid faults. This module provides a vital layer of defence, rated to handle a nominal discharge current of 10 kA. By clamping down on these electrical surges, it protects both the submersible level transmitter and any connected downstream monitoring equipment from damage, preventing costly data loss and equipment replacement.
LMP307 Submersible Hydrostatic Level Sensor & Vented Junction Box
- SKU ID: s1-lmp307-0007
- Part No: 451-4000-1-1-1-1-3-1-010-000
- Sensor Type: Level only
- Level Sensing Range: 0 to 4mH2O
- Reference Type: Gauge / Vented (atm to +P)
- Output Signal: 4-20mA, 2 wire
- Accuracy: 0.35% FS (11-12bit res)
- Installation Type: Submersible probe with flush diaphragm and detachable nose cone
- Housing Material: Stainless Steel 316L
- Diaphragm Material: Stainless Steel 316L
- Media Exposed Seals: FKM
- Cable Type: PVC (70degC max)
- Cable Length: 10
- Cable Length Units: Metres (m)
- Optional Extras: Vented cable junction box with over-volt protect