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ExciteV and VoltSe - CR1000x

Aravindan_K Oct 29, 2021 05:02 PM


I am using CR1000x logger to read output from a Phytos 31 sensor. It's a single ended analogue sensor that can accept input voltage between 2500mV to 5000mV. The output from the sensor is between 250mV and 1250mV depends on excitation voltage. However, the output I am reading from the sensor is only about 125mV.

Below is the code I am using on the data logger for measurement.

ExciteV (Vx1,2500,10000)

The input excitation voltage applied on the sensor is 2500mV, ideally the output value for this should read about 250mV. However, I am getting only 125mV. With the help of a multimeter I have checked both input and the output voltage which reads 2500mV and 125mV respectively. When contacted with the sensor manufacturer I have been told that the output should read about 250mV so I am wondering if am missing something to understand here.

Appreciate if anyone can advise on this.

Thanks & Regards

smile Oct 31, 2021 08:56 AM


this sensor is equal to LWS of Campbell Sci. Please read the CS manual 

However, to make you understand, I think it powered with exiteV and with delay not 0, then when you read it with voltSE it's allready off, try to use the instruction "excite and measure" BRhalf or test with delay 0 in EXITEV which keeps ON until the end of the table so when you read the mV the probe is still powered.

Aravindan_K Nov 2, 2021 11:41 PM


Thanks for the response. The sensor is indeed a LWS (Leaf Wetness Sensor) but of Meter which is compatible with Campbell Sci.

From the product manual of the LWS the sensor require a small delay for settling before a reading can be taken, which is the reason for adding the delay in the first line of the code.

What I am not sure is the execution of the second line of the code. Does the mv5000 mean the maximum output that can be read? This wouldn't make sense as the input voltage from the Excite command is only mV2500.

As I'm already using this code for the last four months and was very recently aware of this issue, I preferably wouldn't want to make any change to the code but to understand it better. In thsi regard, I would appreciate if you/someone could throw light on what the second line on the command is doing that results in the current output. If as an example, the output is factored by 0.5 then I will be happy to correct this while processing the data.

If the code is fundamentally incorrect then I can consider to update it as otherwise the data collected so far will not be usable.

nsw Nov 4, 2021 02:59 PM

The BrHalf instruction recommended in the CS manual, includes a Settling time of 10ms in the "Settling" parameter, which you have included in your ExciteV instruction. So, the BrHalf instruction turns on the excitation, delays for 10ms, makes the measurements and turns the excitation off.

The ExciteV instruction will turn the excitation off as soon as the 10ms period has elapsed, before it then moves on to the VoltSE instruction. So, the sensor will not have the correct voltage applied while you are making the measurement. I suggest you try the CRBasic version in the CS manual, or simply use ShortCut to generate your program and test it, before then copy/paste in to your main program.

Aravindan_K Nov 18, 2021 10:38 PM

This post is under review.

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