LMP305 Borehole Level Transmitter

LMP305 Borehole Level Transmitter

Submersible stainless steel pressure transmitter ideal for geotechnical surveying with a 19mm diameter for measuring hydrostatic water level in bore-holes.

This small diameter level sensor has level ranges from 1 up to 250 metres water column and a 4-20mA current loop output signal.

The LMP 305 bore-hole level sensor has a 316 stainless steel body with IP68 sealing for permanent immersion in water. The sensing element is a miniature silicon chip diaphragm which is mounted inside an oil filled capsule to provide a narrow size with enhanced accuracy & sensitivity performance.

Product Parameters

  • Hydrostatic Level Ranges: from 1 up to 250mH2Og
  • Accuracy: ±0.35 > 4mH2O, ±0.5% < 4mH2O
  • Output Signal: 4 to 20mA current loop
  • Electrical Connections: PUR, PVC or FEP vented cable sealed to IP68
  • Pressure Connection: Removable protection cone
  • Media Compatibility: Stainless steel 316Ti housing, stainless steel 316L diaphragm
  • Dimensions: 19mm diameter
  • Weight: 100 g
  • Special Features: Small diameter, low ranges
  • Special Options: Aluminium cable termination box with PT100 transmitter and/or over-voltage protection

Product Applications

Draw-down testing

Semi-permanent installations for level measurement of boreholes to test the draw-down of groundwater.

  • SKU ID: s1-lmp305-0001
  • Part No: 401-1002-1-1-1-1-3-2-120-000
  • Pressure Range: 100
  • Units: mH2O
  • Reference Type: Gauge / Vented (atm to +P)
  • Output Signal: 4-20mA, 2 wire
  • Accuracy: 0.35%
  • Installation Type: Submersible probe with removable nose cone
  • Housing Material: Stainless Steel 316L
  • Diaphragm Material: Stainless Steel 316L
  • Media Exposed Seals: FKM
  • Cable Type: PUR (70degC max)
  • Cable Length: 120
  • Cable Length Units: Metres (m)

Product Description

For level measurement of fresh-water boreholes with diameter restrictions of less than 1 inch the choice of hydrostatic level sensors becomes much more limited since most are typically 1 – 1.5 inches in diameter.

If you are also planning to measure shallow water levels the low water head pressure introduces another problem, since small diameter pressure sensor diaphragms are less sensitive at low pressures and this has an impact on the output signal and ultimate level measurement accuracy.

So which sensing technology is going to provide the most sensitivity with the smallest diameter? Silicon pressure sensors which incorporate a semiconductor strain gauge have a very small surface areas making them ideal for use inside small diameter pressure sensors. Piezo-resistive silicon strain gauges also offer very high sensitivity to changes in pressure compared to other strain gauge technologies which makes a big difference to pressure sensor performance particularly at lower pressure ranges.

The LMP305 borehole level sensor is 19mm in diameter and includes a silicon sensor element packaged in an oil filled capsule with a thin isolation diaphragm.

The level ranges available for the LMP-305 borehole level sensor begin with 1 mWG and finish with a 250 mWG.

A measurement accuracy of 0.175% full scale best straight line which includes non-linearity, hysteresis & repeatability is specified as standard for the LMP 305 bore-hole level sensor and this can be improved to 0.125% FS if necessary.

The LMP305 small diameter submersible level sensor has a 316 grade stainless steel sensor housing with a 316L stainless steel isolation diaphragm. The electrical interface is IP68 rated for long immersion in water and the cable which has a vent tube running through it to provide the gauge pressure reference is available in a PVC, PUR or FEP outer jacket material.

The LMP 305 borehole level sensor is powered by 12-36Vdc and it outputs a 4-20mA loop signal for transmitting over long distances between boreholes and telemetry stations.

Product Help

Do you have a question about the LMP305?

Cable damage from weight of 240m length

I am using LMP305 stainless steel probe sensor and have to hang it to a depth of 240 metres. The concern I have  is that the combined weight load of the sensor and cable is going to be too much and it will not hold for a long time, and the cable will stretch and become damaged.  What do you suggest to protect the cable?

The LMP 305 with PUR cable has 4 x Aramid cores within the cable assembly. The Aramid has a breaking strength of 100kg. The LMP 305 with 260m cable will be approx. 15kg so this will be fine.

Also bear in mind that the buoyancy of the submerged part of the cable and sensor will reduce the total weight so it could be much less than 15 kg.
LMP305 PUR cable cross section

Atmospheric compensation

Does the LMP305 miniature borehole pressure transmitter use a vented cable? If cable is not vented, how is the atmospheric pressure compensation done?

Yes the cable fitted to the LMP305 is vented and connected internally to the reference side of the sensing diaphragm, therefore it will self-compensate for changes in atmospheric pressure.

Atmospheric compensation of borehole pressure sensor

For those sensors which do not have vented cable, the only way to compensate for atmospheric changes is to use a barometric reference at the water surface and subtract the measurements from the water level readings.

Related Documents

Specification data sheet


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