I'm using some older equipment here.
I have a Geokon 4800 vibrating wire pressure cell, a AVW1 interface, a CR10x datalogger, and to read it all i'm using a SC32B to USB.
http://www.geokon.com/content/manuals/4800_Earth_Pressure_Cells.pdf
I'd like to know if I can just use a generic measurement instrument type in PC200w to get a reading off the pressure cell and thermistor.
Would it be a single-ended, or differential voltage? From some of the wiring diagrams I've followed the 4800 and thermistor are connected to the AVW1 and the interface connects to the 1H, 1L, E1, AG, 5V, and G channels which looks more like Single-ended or even half bridge. Anyone had any success with this?
Alternately, I have had success reading the pressure cell and thermistor with a very old version of Canary's multilogger so I know my wiring and equipment is all good.
There's a wiring diagram on page 8 of this document which I followed but without the multiplexer.
http://www.slopeindicator.com/pdf/manuals/cr10-and-vw-sensors.pdf
And here is some guidance I used with the old multilogger v1.4 software.
http://www.canarysystems.com/nsupport/canary_san13.pdf
Problem is that's on an old computer that I can't take with me into the field.
Any help would be appreciated.
Hi Max,
A "vibrating wire" sensor uses a whole different approach to capturing a reading,so for the pressure output you won't be able to use a standard single-ended or differential voltage measurement, or half/full bridge measurement (on the CR10X) to get the results you want. You will need the AVW1, or some newer hardware (like the CR6 or AVW200) for that process.
If you want to use the CR10x without the AVW1 (or AVW200) you could purchase a Geokon 3500 or similar that doesn't use a vibrating-wire element within the sensor. However it may not have the same specs/stability that you want. The specs would have to be scrutinized.
Your sensor has 4 leads plus a shield/ground from what I can tell.
Two of those leads are internally connected to the coil of the sensor transducer (which will be a vibrating wire measurement in Hz that maps to earth pressure) and the other two leads are connected to a thermistor (RTD) within the sensor. The two "T" connections on the AVW1 are for attaching the thermistor leads and the two "C" connections are for the coil leads.
For more recent Geokon sensors, the 2 coil leads would be black and red, and the two thermistor leads would be green and white. If you have a different color scheme there are ways to identify the leads using a multi-meter.
You can use a standard half-bridge measurement (with just the CR10X, no AVW1) on the thermistor leads (green&white) to obtain a resistance which is then converted with the Steinhart-Hart equation to obtain temperature in Degrees Celsius. However that is the secondary measurement (temperature correction) and not the primary pressure output of the sensor.
To obtain a pressure reading, your hardware needs to excite the coil leads (red&black) with a specialized excitation technique (sweep, not constant voltage) and then read back an oscillating time-series signal and capture it. The time-series signal is then analyzed to obtain a frequency in Hz. The frequency in Hz is the primary output of the sensor. The signal capture needs to resolve high frequencies up to 6000 Hz.
The 4800 manual will give guidance/factors for converting your Hz/Frequency output into units of pressure (i.e. calculation equations with frequency as the input).
The specialized excitation technique, capture of time-series waveform, and frequency analysis are why the AVW1 device is used with the CR10X in your measurement system.
If you don't want to buy any new hardware, then your task is to write a program for the CR10X that utilizes the AVW1 to make a vibrating-wire measurement on your sensor.
Shortcut for the CR10X doesn't support this. However we do have information about the AVW1 on our website:
http://www.campbellsci.com/avw1
And the manual is here (sample programming included):
http://s.campbellsci.com/documents/us/manuals/avw1.pdf
You should probably contact your local CSI rep and they should be able to help you get an Edlog program going that does what you need.
However, I would like to strongly recommend that you obtain some new hardware.
This brochure explains our patented VSPECT technology:
http://s.campbellsci.com/documents/us/category-brochures/b_vspect.pdf
With the AVW1 there were some external noise interference/limitations that we were able to overcome with the newer AVW200 and later products (CR6, CRVW3). That is why we sell those items now instead of the AVW1/AVW4.
The simplest way for you to move forward is to purchase a CR6. That would replace both your CR10X and the AVW1. If you purchased an AVW200 (cheaper) you would have to have a CR10X program that makes an SDI-12 reading (may be more effort than it is worth). ShortCut can be used to generate CR6 programs that measure Vibrating-Wire sensors. Once again, I would contact your Campbell representative to discuss this.
I hope this helps.
http://s.campbellsci.com/documents/us/manuals/avw1.pdf
The Geokon 4800 is very similar to the Geokon 4500 from a measurement perspective. The only essential difference is that different gage factors or polynomial constants are used to convert from frequency/Hz to pressure.
Also note that Geokon uses "Digits" as the primary frequency input instead of Hz. It is easy to calculate "Digits" by simply squaring the frequency (in Hertz) then dividing by 1000.
Digits = Hz*Hz/1000 = f^2/1000
Geokon typically refers to this digits reading as "R" or "R1".