FAQs
Do I need to apply corrections for changes in atmospheric (barometric) pressure?
The VW piezometer is a sealed unit that is sensitive to any pressure on its diaphragm. It does not distinguish between pressure of the atmosphere and pressure of the water. It responds to both. However, whether this is important or not depends on your application.
Suppose you suspend the piezometer in a standpipe or water well that is open to atmosphere. The piezometer will report the combined pressure of the water and the atmosphere above the water. If your intention is to monitor the level of water in the well, you must correct for variations in atmospheric pressure.
Now suppose you seal the piezometer in a borehole to monitor pore-water pressure. In this case, the pressure acting on the diaphragm is only the water pressure at that depth. Thus you would probably not correct for variations in atmospheric pressure, even if you later found a relation between atmospheric pressure and pore-water pressure.
You can find more about this subject and how to use barometer readings to make corrections in the VW piezometer manual.
How do I convert the units my Geokon readout displays to values in Hz?
Geokon (and other manufacturers) use digits in their calculations:
digits = Hz^2 / 1000
Therefore, to convert digits to Hertz, multiply digits by 1000 and take the square root of the result.
How are water level readings affected by changes in atmospheric pressure?
Atmospheric pressure may vary as much as 34 millibars (0.5 psi) during the day. This is equivalent to apparent water level changes of ±150 mm ( ±6 inches). Even larger variations can occur during stormy weather.
What tests can be performed if I am having trouble getting readings?
The tests below can be performed with a handheld multimeter.
If there is no reading: Set your handheld multimeter to a low range (less than 5k ohm).
- Measure the resistance between the two VW wires (orange and white-and-orange). A normal reading should be about 300 ohms. If the reading is very high or infinite, the coil is probably burned out (typically from lightning damage). If the reading is very low, the cable is probably damaged.
- Measure the resistance between the temperature sensor wires (blue and white). Thermistors should read about 3000 ohms. RTDs should reading about 2000 ohms. If the reading is very high or infinite, the temperature device is burned out. If the reading is very low, the cable is probably damaged.
If the reading is unstable: Set your handheld multimeter to a high range (10 or 20 M ohm).
- Measure the resistance between a VW wire and a Temp wire. The reading should very high or infinite.
- Measure the resistance between any of the colored wires and the drain (shield) wire. The reading should be very high or infinite.
- Measure the resistance between the shield wires of two VW sensors. The reading should be very high or infinite. A lower reading indicates the presence of a ground loop. Check that each instrument is isolated from the others when it is read. This may require rewiring your multiplexer. Contact the factory for suggestions.
- Some other sources of trouble may be electrical noise from nearby power lines or motors. A over-ranged or shocked instrument may also exhibit these problems.
What lightning protection is built into the VW piezometer?
We have wired a zener diode in parallel with the coil (which is used to pluck the wire). The diode is rated for 1.5 KVA peak pulse, with conduction starting at 10 volts.
What data formats does Atlas accept?
Atlas accepts only text files. The most common formats are listed below:
| Campbell Scientific Table Based TA05 Format Description: “yyyy-mm-dd hh:mm:ss”,recno,value1,value2,value3,value4,value n, Example: “2008-01-06 12:00:00”, 3068.8,11.5,3045.5,12.6, Notes: – date stamp is quoted (” “) – date is fixed: yyyy-mm-dd. No variations are allowed. – date separators are hyphens ( – ) – recno is a record number. Atlas does not use the number, but requires at least a blank field. – decimal character is a dot ( . ) – value separators are commas ( , ) – TA05 normally has a header. Atlas ignores the header, if present. |
| Serial Number Format Description: “yyyy-mm-dd hh:mm:ss”, recno ,”serial1″,value1,value2,”serial2″, value1,value2,value3, Example: “2011-10-27 22:00:00”,“33853”,12.86,7.137,“15766”,12.77,0.558,6543, Notes: – Same as Campbell table format, but has embedded serial numbers. – date stamp, decimals, and value separators are same as in Campbell format above. – serial numbers are quoted. Atlas uses serial numbers to assign values to the proper sensor. – each serial number can be followed by an arbitrary number of values (if necessary). |
| Atlas Format Description: dd/mm/yyyy;hh:mm:ss;value1;value2;value3;value4 Example: 01/27/2008;12:00:00;3068.8;11.5;3045.5;12.6 Notes: – date is separated from time by a semi-colon ( ; ). – date order can be: dd/mm/yyyy or mm/dd/yyyy or yyyy/mm/dd, etc. – date separator is a forward slash ( / ) – decimal character is a dot ( . ) – value separator is a semi-colon ( ; ) |
How do I read VW sensors with a CR1000x or CR350 datalogger?
Neither the CR1000X nor the CR350 can read VW sensors directly. A VW module (AVW200) must be used with these loggers.
How do I convert RTD or thermistor readings to degrees C?
Choose a formula from the table below:
| Vibrating Wire Sensors with AVW200: Where Ohms = reading in ohms Coefficients for Thermistor: A = 1.401e-3 B = 2.377e-4 C = 0.00e0 D = 9.730e-8 Formula for Thermistor: Deg C = 1/(A+B*LN(Ohms) + C*LN(Ohms)^2 + D*LN(Ohms^3)-273.2 Coefficients for RTD: J = -23.50833439 K = 227.625007 L = -341.217356417 Formula for RTD: Deg C = (J*((Ohms/1000)^2)) + (K*(Ohms/1000))+(L) |
| Vibrating Wire Sensors with AVW1, AVW100, or AVW4: Where VT = reading in volts Coefficients for Thermistor: A=43.089 B=-240.91 C=544.27 D=-611.59 E=378.11 F=-104.78 Formula for Thermistor: Deg C = A*(VT^5) + B*(VT^4) + C*(VT^3) + D*(VT^2) + E*(VT) + FCoefficients for RTD: A=-435.97 B=1904.4 C=-3442.5 D=2412.6 Formula for RTD: Deg C = A*(VT^3) + B*(VT^2) + C*VT + D |
| MEMS or EL SC Sensors: Where VT = Thermistor reading in volts: Coefficients: A=9.3219 B=-54.3038 C=131.165 D=-161.2568 E=137.7711 F=-37.7705 Formula: Deg C = A*(VT^5) + B*(VT^4) + C*(VT^3) + D*(VT^2) + E*(VT) + F |
| 4-20mA Sensors: Where VT = Thermistor reading in volts: Coefficients: A=43.089 B=-240.91 C=544.27 D=-611.59 E=378.11 F=-104.78 Formula: Deg C = A*(VT^5) + B*(VT^4) + C*(VT^3) + D*(VT^2) + E*(VT) + F |
I want to place my CR1000x and AM1632 multiplexer in different locations. How far apart can I place them?
We usually recommend that the multiplexer be placed close to the CR1000x, but if you must separate them, here are some points to consider:
1. Power: The CR1000x must supply power to drive the relays on the multiplexer, so you must check for a voltage drop caused by the resistance of long cables. See the AM1632 manual for power requirements.
2. Digital Ouput and Pulse: The CR1000x sends a digital signal to reset and clock the relays. The duration and level of this signal can be degraded by long cables. See the AM1632 manual for required voltages.
3. Signal Degradation: The signal from the sensor doesn’t stop at the multiplexer. It continues, unamplified and unfiltered, through the multiplexer all the way to the CR1000x. Long cable lengths are subject to RF noise from the environment and resistance from the cable.
Is there a way to connect a CR1000x to my SCADA system?
There are two ways to interface a CR1000x to a SCADA system.
- Make a hardware link via RS232 using the Modbus protocol to interface to HMI (Human Machine Interface) of the SCADA system.
- Make a software Link using PC-OPC from Campbell. SCADA system has to be compatible with OPC (Ole for Processing Control). Use Loggernet and prefered telemetry option. Loggernet acts as server, with data in Cache. PC-OPC resides on PC and acts a client. PC-OPC goes to server cache, retreives data, then makes it available to HMI, essentiall providing a software ‘bridge’ to HMI.
Can I use a terminal program to communicate with the VW MiniLogger?
Yes. There is also a terminal emulator built into the MiniLogger Manager program. Please note that the MiniLogger’s terminal mode is simply for checking the functions of the logger and not intended to support access by other automated means. More about Terminal Mode
What is the minimum radius bend for piezometer signal cable?
Where the cable exits the borehole, we’re planning to route it into PVC pipe.
The standard PVC sweep used by electricians in the construction industry should be fine. These typically have a 6-inch radius. The problem is not the minimum radius itself, but the friction in pulling cable through the bend. Also, it is a good idea to allow a little slack cable for settlement and other movements.