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et3500 driver rounding error

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Thanks for the quick response. Looks like you're right on this. Till now I abandoned LabView and started controlling it manually to provide the relevant power to the source, I gues I just didn't understand how eurotherm worked to begin with. More reading for me I gues :).

 

I looked at the temperature controll and monitoring example as you mentioned, and from my understanding:

 

1. It initialises Eurotherm (for communication purposes etc.) - This I understand

2. It turns Eurotherm in "Configuration Mode" (this I'm asuming is done in order to set the PID parameters that are done afterwards) - I understand this aswell.

3. It provides the "Low Set-Point Limit of -10 deg." - Don't understand the reason why are there "lower and Higher" limits to a set point.

4. It provides the "High Set-Point Limit of 510 Deg." - Same as above

5. Configures the Loop Set-Up Parameters and makes the derivitive a "PV" type. - On the example, I could choose either "PV" (as they did) or "Error". What would the difference be.

 

I gues these points from 3 - 5 are all used to set up the PID parameters (the bit I don't quite understand Smiley Sad).

 

Just so that you have a better understanding, I have a globar that I want to heat to about 900 deg., and an R-Type Thermocoupler to read the temperature.

 

I made a simple program using 4 setpoints (i.e. to steady increase the temperature, then wait for a period of time on the temperature mark i.e. 900 deg. then a steady decrease of temperature to finally bring the whole process to a halt. 

 

Sorry for making this a long post. I wouldn't want to intrude on your free time, but thank you for yuor help.

 

Regards

 

Kas

 

 

 

 

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Message 11 of 14
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I've made an example for you, showing how to set the PID parameters and read the temperature.

It's a modified version of one of the examples that come with the driver. I removed all the alarm components (they were acting up on my machine) and replaced the measurement component with a direct read from register 22727. I was originally using register 21276, but for some reason I stopped using it and switched to 22727. I can't remember why, but this seems to work 🙂

 

 


@zerotolerance wrote:

2. It turns Eurotherm in "Configuration Mode" (this I'm asuming is done in order to set the PID parameters that are done afterwards) - I understand this aswell.


After initialization, the Eurotherm is put in configuration mode. Some settings can apparently only be changed in configuration mode. After these settings have been set, notice that the instrument is put back into "Normal" mode - before the PID parameters are set.

 

In configuration mode the setpoint limits are set to -10 and +510 degrees, but later some similar settings are set to 0 and 500 degrees. The limits on the setpoints are probably some sort of safety measure. I don't know why they are set twice though.

 

I don't know what the difference is between "Error" and "PV", but I'm guessing it's related to the derivative term of the PID control. The limits on setpoints have nothing to do with the PID parameters. The PID parameters are set by the very last box before the loop starts, this is the only box that has to do with the PID parameters. The three parameters are called "Proportional band", "Integral time" and "Derivative time".

 

Have a look at this page: http://www.expertune.com/tutor.html

It helped me a lot. 

 

 


@zerotolerance wrote:

I made a simple program using 4 setpoints (i.e. to steady increase the temperature, then wait for a period of time on the temperature mark i.e. 900 deg. then a steady decrease of temperature to finally bring the whole process to a halt.  


In my program I am continuously sending setpoints to the Eurotherm. I increase the setpoints linearly, and the Eurotherm keeps up the temperature. This way I can increase my temperature linearly at a custom rate, and make beuatiful heating ramps 🙂

 

Hope this helps.

 

 

Message 12 of 14
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Hi \

I have the same probelm, the PV readings is rounding. I can only see the address 360 not 21276 or 21277 as you have mentioend. I am using 3508.

 

Thanks

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Message 13 of 14
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thank you for sharing your program. 

I found that the READ sub-vi has some trouble. Is it possible to add this sub-vi ? 

When I use the standard et3500 read.vi into your program, then I got an output that is 10^24.

If I run the standard et3500 program with the standard et3500 read.vi, in the same conditions, I get the correct PV. 

So I guess you have modified the et3500 read.vi, but it was not attached or included. 

 

Yours

Laurent

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