As a datalogging novice I am planning a datalogging system with multiple EC sensors at near constant temperature .
The Campbell dataloggers are to my knowledge the only suitable dataloggers for EC .
The Campbell 354 EC sensor and 354A connecting box are not suitable for me .
I need only 1 temperature measurement.
I will use custom EC cells , with cell constant of about 1 , comparable with the Soil Moisture Equipment Corp EC sensor type 5000 , but without temperature compensation.
I will check Cell constant , wiring etc by immersing sensors + wiring in water with known EC ,1-4 levels ,
EC of about 0.1 , 1 , 10 and 50 mS /cm [ sea water].
Which EC range can be used by this method ?
In the low end and high end I need less than 10 % precision , in the middle range better than 5 %.
Raw data are stored in the datalogger . Results are calculated in Ecxcel file by using the calibration data .
You use 2.5 V exication for EC ,why , standard is about 0.25 V in EC transmitters , why ?
What is the frequency of voltage reversal ?
Can I change that frequency ?
Can I measure during more than 2 voltage reversals to eliminate outlyers due to other equipment or the averaging time and method .
Can I choose the moment of measurement after voltage reversal?
Which dataloggers are suitable , old and new.
Where can I find programming examples , I found none
in the manual :(ftp://ftp.campbellsci.com/pub/csl/outgoing/uk/manuals/cr1000_csi.pdf).
I understand the function of the isolation capacitors , but why 2 on both conductors ?
You advise shielding , Is it important in modern labs with high energy use and high power Na and Hg lighting and electric motors and relevant for precision
I found no references to EC in the forum .
Thank you in advance,
,
To answer some of your questions. Our own 547 sensors are limited in their upper range of concentration measurement partly because of the risks of corrosion to the stainless electrodes, partly because the corrections needed to get a good measurement become large and partly of the physical constuction of the sensor.
The correction effects become large because of the effective AC frequency is only about 700-1400 Hz (the latter with optimal settings in our newer loggers). This is a bit too low to stop all ionization effects and those effects vary with the constituents of the water (which is usually not constant). With our newer loggers you can set a settling time of 100 microsec and integration time of 250 microseconds to get to the higher frequency.
In terms of the excitation voltage, you can set this to whatever you like as long as the input range is set appropriately. I am not enough of an expert to say whether this will reduce the ionization effects anymore than a proportional reduction.
In terms of noise averaging you can do this simply by repeating the measurement in a loop and mathematically averaging the reading or applying some other statistical technique. If you cannot screen the probe you will need to use this technique to get rid of noise.
Regarding the capacitors, there is one in each leg to prevent any DC current flowing through the circuit from the sensor elements to some other ground reference in the solution being measured (which is a possibility in a field installation). That current would usually cause the sensing element to degrade in some way due to electrolysis.
* Last updated by: aps on 5/31/2011 @ 6:33 AM *