Read raw mV value from DrDAQ's pH channel from the SDK

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MaximeDL
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Read raw mV value from DrDAQ's pH channel from the SDK

Post by MaximeDL »

Hello,

Is it possible to retrieve the raw mV value from the pH channel of a DrDAQ from the SDK?

I'm writing my own C# application and need access to the raw mV value from a pH probe connected to he pH channel, not the pH calculated by the DrDAQ.

Thank you,
Maxime

Gerry
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Re: Read raw mV value from DrDAQ's pH channel from the SDK

Post by Gerry »

Hi MaximeDL,

Last time I checked, this was done in the Driver (in order to provide Temperature compensation based on the sensed connection of the DD100 Temperature sensor to the relevant input channel). That was for PicoLog 5, but I wouldn't expect that to be different for PicoLog 6.

However, one of our users has written a post on how to perform very accurate pH measurements, including getting accurate mV values from the pH sensor, which I would encourage you to look at here: topic27111.html. He also, includes the ability to compensate for temperature with an alternative (low mass NTC sensor) to the DrDaq standard DD100 sensor.

When using the pH sensor you are advised to re-calibrate it for any kind of usable accuracy (in the DrDaq User Guide) so you may as well use the procedure, suggested in the link, to create a function or table that provides an accurate conversion, which you can then add a 'calibration' function to.

Regards,

Gerry
Gerry
Technical Specialist

MaximeDL
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Joined: Thu Mar 25, 2021 2:22 pm

Re: Read raw mV value from DrDAQ's pH channel from the SDK

Post by MaximeDL »

Hello,

Thanks for pointing out to this thread. I did read through it but without paying enough attention and didn't realise it pointed out ways of getting the mV value.

However, for several reasons, I feel like the solution described in that thread doesn't suit my needs.

I don't want to use the DrDAQ for temperature adjustment. A few things are not clear to me. What happens if I don't plug any temperature sensor into EXT1 ? Is that right to assume that the DrDAQ will read th pH at a fixed temperature of 25° ? Do I need to make configuration/hardware modification to ensure no pH compensation happens?

My understanding is that the calibration can only be performed through Picolog HMI. That won't be possible in my application. I'm really just interested in getting the raw mV value from my probe.

My hope is that if no temperature probe is connected to EXT1, DrDAQ will use a default temperature of 25° which would allow me to use the expression pH = 7-(Ve/ 59.16) to calculate the raw mV value. I will create my own pH curve with an automated calibration sequence.

Sorry for the late reply,
Maxime

MaximeDL
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Joined: Thu Mar 25, 2021 2:22 pm

Re: Read raw mV value from DrDAQ's pH channel from the SDK

Post by MaximeDL »

Can anyone confirm my assumptions and/or answer my questions above ?

Can anyone describe how to calibrate DrDAQ through the SDK ?

Gerry
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Posts: 988
Joined: Mon Aug 11, 2014 11:14 am

Re: Read raw mV value from DrDAQ's pH channel from the SDK

Post by Gerry »

Hi MaximeDL,

Sorry for the delay in responding. This one took awhile to resolve because it required sifting through legacy code in the driver for the DrDaq, which was written some time ago (and our development team are over extended, pushing hard to get the next version of our Software out, among other things).

So, the answer is that we can confirm you suspicions, in that, if there is no Temperature Probe detected, the Driver will use a default temperature value of 25°C.

I'm not sure what you're referring to when you say "My understanding is that the calibration can only be performed through Picolog HMI". As explained on page 14 of the DrDaq User Guide (see here: https://www.picotech.com/download/datas ... -guide.pdf) the calibration is just done using a test procedure. In order to implement the correct scaling the manual describes how to apply scaling in PicoLog 5. However, if you are writing your own application then you can just apply your own scaling to the captured values using a lookup table filled with scaling values found from the results of your calibration.

Regards,

Gerry
Gerry
Technical Specialist

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