piezometer reading (vibrating wire type)

[WyoEng]

I've got to read the signal from a vibrating wire type of piezometer (made by Geokon, model 4500MLP).  Has anyone had to read signals from a vibrating wire piezometer, and if so, how did you go about it?  From what I read in the documentation, it sounds to me like the signal is a frequency.  Does this mean it sends out a pulse count, and if so, how do I actually get viable data?  I couldn't find any discussions or documentation on piezometers on the NI website, and the company that puts out this piezometer has their own daq system, which I don't want to purchase (I'd rather use NI daq hardware and LabVIEW softare).  I'd really appreciate any help or advice anyone can give me on this matter.

(link to company's website and to the multilevel piezometer of interest:  http://www.geokon.com/multilevel-piezometer/)

[johnsold]

The signal is a frequency, but to get it they excite the wire with a variable frequency burst and then measure the frequency of the response.  They do not appear to specify the impedance of the excitation or read coils nor do they indicate how powerful the excitation must be or how strong the return signal will be.  It looks to me as though your would have a lot of reverse engineering to do if you want to make your own signal conditioning circuits.

Lynn

[WyoEng]

Lynn,

Thank you for the explanation of how this works.  While your answer is not what I was hoping for, at least it helps me to be realistic about what I need.  I don't think I will be reverse-engineering this--I will probably go with the company's accompanying system for the piezometer.

[Henrik_Volkers]

Looking at the Readout Box manual, it seems that the exitation is +-5V or 0V-5V 🙂

B&K build something similar in their chargeamplifier to detect the resonance frequency of the transducer .

Via relay it switches the sensor between exitation and reading.

Switch to exitation and apply a 5V pulse followed by a -5V pulse  (pulse length about half the expected freq here ~1k -> 500µs 5V followed by 500µs -5V)

switch to sens mode and read the declining frequency

Reed relays switch in less 1mS.

I did a resonance measurement on a piezo accelerometer by reading the the voltage over the sensor (10G impedance) while exiting with a 10Meg 2Vpp sweep.

Maybe it's worth to try it with a 10:1 probe (10M input impedance) and a 1Meg source....

You gave no hint on your equipment available ... however maybe a soundcard line out with 1Meg coupling  and a 100nF and 10Meg to the mic input is enought for a quick and dirty try 😉

And while we are in a LabVIEW forum

http://www.zeitnitz.de/Christian/scope_de

has done already a software in LabVIEW that seems to fit for a test 🙂