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DrDaq interface with the real world

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DrDaq interface with the real world

Postby sbillett » Tue Jan 28, 2003 1:28 pm

Hi

Question 1

I am writing an appilication to control the PH in a Marine Fish Tank in VB, Is it possible to interface more than one PH probe to a DrDaq board ie through one of the ext ports ?

Question 2

Can anyone advise me on how to use the Digital Output off the DrDaq Board I can switch it on and it supplies 4.5 Volts But I presume the Ampage is to low that is why it wont open the relay on my PLC.

I presume I will need some form og line driver to increase the out put, But I am not an electronic engineer (Help) :cry:


Thanks in advance

Steve
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Postby matthew » Wed Jan 29, 2003 11:25 am

Hello Steve,

Its not really possible to change the External channels into a PH probe input. The main reasons for this are that the PH Probe is bi-polar (approx. ±576mV) and the Ext inputs are unipolar (0 to 2.5V). Also, the PH input is heavily filtered, so you would need to apply this filtering yourself.
I would not take this on unless you are reasonably confident with electronic circuit design.

The current through the Digital Out is supplied by the PC, and it is usually very low. You could use an external power supply and an amplifier, but again, you would need to be reasonably confident in electronics (sadly we don't have any circuit designs for this here).

Sorry I can't be more optimistic with this :(.

Kind Regards,
Matt Everett

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Marine PH control

Postby sbillett » Thu Feb 06, 2003 9:41 am

Hi Matthew

Sorry had the flu bug, so I was not checking my mail. Thanks for the info.

I really need to test for 2 pH values so I will enlisting one of my electronic enginner friends to help convert the Voltage input 0-5V into a second pH port. I presume that this port is also unipolar but 0 to 5 Volt

Questions.

1.
Can I find a circuit diagram of the DR Daq somewhere, I don't want to pull the foam off my unit in case it invalidates the warrenty. I want to try and see how your are doing the filtering.

2.
For your main pH port, I need to use pH Temperature Compensation from one of the external Temp ports. Rather than me recreating the wheel, can you supply me with the pH to Kevlin relationship formula that you are using in your software.

I presume that is where you are converting the value and not on the logger board itself. From what I understand its a straight line graph presuming that the pH unit gives out 59.16 mV @ 25 degrees C ( 298 Kelvin ) and 74.04 mV @ 100 degrees C (373 Kelvin)

But you formula would be very helpfull


3.

In a similar fashion what is you formula or constant link Raw to Measured to allow for calibration of the probe.


Thanks in Advance

Steve

Sorry to ask these questions, but I realise now that I haven't used my maths for over 25 years and the brains not as good as it was.
sbillett
 

Postby matthew » Wed Feb 12, 2003 10:29 am

Hi Steve,

Unfortunately, I can't release circuit diagrams (for obvious reasons). We're selling a packaged product, and a lot of development time has gone into them so I can't send out operational information on the software / hardware in a lot of cases.

The help files do contain a wealth of information though, so I would have have a look at these for the information that we are allowed to give out.

The best way to proceed with this is probably just to buy a second DrDAQ and run them in parallel. The amount of time you spend developing the electronics will certainly outweigh the cost of a second unit.

Sorry, that I can't give you all of the information that you would like.

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Matt Everett

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I understand your problems But......

Postby sbillett » Wed Feb 12, 2003 11:30 am

OK :( I understand your problem and will deal with it myself somehow, even buying a second module but that means a second parrell port must be available. Unless you have a way of chaining them together.

I need to use pH Temperature Compensation from one of the external Temp ports instead of the internal Temp. Can you please advise how this can be done. ( I have looked in the help file and cannot find any clue)

I will need to take raw data from the pH Probe channel (5) add add my own compensation or need to know how to compensate for the differance in temp between an internal & external .

Thanks

Steve


PS I have sorted the DO power problem now. ( My electronics is getting better)
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Postby matthew » Wed Feb 12, 2003 1:24 pm

Hi again Steve,

I'm afraid you won't be able to do the temperature compensation like the built in pH channel, because this all goes on inside the software. The only suggestion I could make is to use Settings | Calculated parameters to perform the calculations in real time (the help file details how to set this mode up). I have found some approximate temp / pH compensation info: The pH increases approximately 4% for a 10degC rise in temperature.

A second parallel port is no problem, we sell both Dual Parallel Port PCI cards and USB Parallel Port Adapters ourselves. Just phone us up to get the prices and place an order.

I would personally be inclined to go for the second DrDAQ.

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Matt Everett

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