How Is Vibrating Wire Piezometer Installation Done?

Vibrating wire piezometer is used to measure the pore pressure in heavy structures like earth/rock fill dams and mass concrete during construction and for long term monitoring after construction is over.

The vibrating wire piezometer installation procedure requires complete knowledge and assistance. Before starting with the procedure, let’s first look at the list of tools needed for the installation.

Tools & Accessories Required for Vibrating Wire Piezometer Installation

  1. Soldering iron 25 watt
  2. Rosin 63/37 solder wire RF-3C, 30 swg
  3. Thread sealant (Loctite 577 or equivalent)
  4. Cable jointing compound
  5. Acetone (commercial)
  6. Spanner 20/22 and 26/28 and pliers 160 mm
  7. Hacksaw with 150 mm blade
  8. Cable Cutter
  9. Surgical blade with holder
  10. Wire stripper
  11. Bent nose plier (internal)
  12. Pouring funnel
  13. Stainless steel rod 5 mm φ, 150 mm length and Spatula
  14. Rotary tin cutter
  15. Fixture for jointing up to six piezometers
  16. Toothbrush
  17. Cloth for cleaning (lint less)
  18. Geo-textile bag (150 mm x 250 mm) with integral tying lace to contain the piezometer
  19. Digital multimeter
  20. EDI-51V portable readout unit

Vibrating Wire Piezometer Installation Procedure

Preparation of sensor before Vibrating Wire Piezometer installation

Here are the general instructions for Encardio-rite Vibrating Wire Piezometer Model EPP-30-V.

  • To give access to the four-pin terminal, it is required to remove the cable joint housing from the cable end of the sensor. The terminals marked with red and black colors are internally wired to the coil of the magnet assembly which, exists inside the sensor. On the other hand, the other two terminals are used to measure temperature with the help of a thermistor. The terminals can be cleaned using a toothbrush.

vibrating-wire-piezometer-installation

NOTE: Acetone can be used to clean the sensor except the terminals. Using acetone for cleaning the terminals as it destroys the glass to the metal seal.

| Also Read: Vibrating Wire Piezometer – Types and Operating Principle |

Checking the working of the sensor

  • The coil resistance measured by a digital multimeter between the red and black pins should lie between a particular ranges for each kind of Vibrating Wire Piezometers. For Model EPP-30V, the resistance should lie between 120-150 Ohm. On the other hand, for Model EPP 40-V and VW Piezometer EPP-50V, the resistance should lie between 130-170 Ohm. It is important to determine the resistance at room temperature from the thermistor temperature resistance chart.
    To judge the resistance accurately, it should be equal to the resistance between the pins marked green and white. For example, if the room temperature is 25oC, the resistance would be 3,000 Ohm.
  • Make sure that the resistance between any lead and protective armor is greater than 500 M Ohm.
  • The next step is to connect the sensor with Encardio-rite Model EDI-51V Portable Readout Unit and switch it on. The display should show the reading in the following manner- Freq: 2629.8 Hz. The frequency measure may vary according to the transducer connected to the indicator.
  • When working with vibrating wire piezometer installation, the initial reading (offset) of the frequency displayed on the portable readout unit should be stable.
  • A cross-check can be done for Encardio Model EPP-30V to verify whether the sensor is reacting to the changes in pressure. This can be done using the following steps:
  • With the help of a locking nut spanner, remove the filter of the vibrating wire piezometer.
  • Put pressure on the diaphragm using your thumb. Verify whether the frequency reading on the indicator decreases.
  • The change in the reading assures that the pressure on the diaphragm is successfully transmitted to the vibrating wire sensing element.
  • Every Encardio-rite sensor is provided with a test certificate which lays down the relationship between output and applied pressure. To start with this procedure, change the readout unit display to frequency2 mode.

The Zero Reading in Frequency2 for Vibrating Wire Piezometer Model EPP-30V and EPP-40V should not vary from current zero reading by more than 100 (x 103) divisions and 250 (x 103) divisions respectively after consideration made for the difference in temperature, barometric pressure, height above sea level, and actual cell position (whether standing up or lying down)
test-certificate-epp-30v vibrating wire piezometer

For example, in the test certificate, the zero reading in frequency2 for the Encardio-rite Model EPP-30V at the time of dispatch is 6452.6 (x 103 Hz2). Assuming that the temperature and barometric pressure is the same at the place and time of installation and sensor is placed lying down, reading in frequency2 should be between 6,352.6 and 6,552.6 (x 103 Hz)

test-certificate-epp-30v vibrating wire piezometer

| Also Read: Piezometers: Types, Functions, & How it Works? |

Connecting the cable to the Vibrating Wire Piezometer while Installation

The next step is to connect a required length of cable to the Encardio-rite Vibrating wire Piezometer model EPP-30V or EPP-40V piezometer as described in the operating manual on cable jointing WI-6002.11 or extend the cable of Model EPP-50V as needed.

NOTE: While unreeling the cable, the cable drum should always be turned so that the cable is set on the flooring. Avoid unreeling the cable by pulling on the cable itself as it may damage the internal conductors from the excessive pulling and strain. Another thing to keep in my mind is to never unwind the cable from any one side of the drum.

Cross-checking the working of the sensor

Verify the working of the sensor once more following the procedure stated before.

NOTE: Add cable resistance when checking resistance between the leads after the cable jointing. For the model CS 0401 cable, the resistance is 26 Ohm/km, and for the model CS 0406 cable, the resistance is 48 Ohm/km. (multiply by 2 for both leads). In case any other cable is used, make sure to do the necessary addition in resistance value.

Saturating filters

  1. Remove the filter from the piezometer using a bent nose plier. Boil the filter in a container for about 15 minutes. Let the filter saturate in the water and wait for the container to cool down to room temperature.

NOTE: Each Encardio-rite Vibrating Wire Piezometer has a different system of removing the filter. The Model EPP-30V filter can be removed by opening the locking nuts. For VW Piezometer Model EPP-40V, the filter is removed by pulling out the filter holder, whereas, for Model EPP-50V, the filter is removed by unscrewing the conical top.

  1. To re-assemble the filter, dip the piezometer head inside the water. Take great care to keep the water that is enclosed between the diaphragms and filter is not leaked out of the sensor during any movement. It is important to bag the sensor in de-aired water until installation.

CAUTION: Leaking of de-aired water out of the piezometer will lead to an erroneous reading of pore pressure as an airlock develops behind the filter. If by any chance the water leaks out, repeat the process making sure that ‘O’ ring provided sits properly in its position, and the locking nut is properly tightened.

NOTE: The assembled piezometer should be bagged in de-aired water to maintain saturation until installation.

NOTE: Follow the above procedure in high and low air entry filters.

The installation procedure needs to be carried out with great care and precision as it may lead to dubious reading. Make sure to go through all the steps stated above.

This was all about the Vibrating Wire Installation Procedure. If you have a query or suggestions to make, feel free to drop them in the comments section below.

Related posts

Leave a Reply

Your email address will not be published. Required fields are marked *

four × four =