Calculate Enthalpy values from Temperature using lookup table method

[SuLAB]

Hello,

I am reading data from 4 temperature channels on a scanner using RS 232 of a Vapour Compression Refrigeration System.

Data from each of the channel is stored into an array. 

Every temp.channel has different temp. range ----- for eg. Suction temp.is below 0 degree celcius and discharge temp.is kind of above 100 degree cel.

Overall temp.range for all the 4 channels would be from -50 to 500 degree celcius

Now, I want LabVIEW to automatically generate Enthalpy values for a given temp.from a "Lookup table" kind of thing.

For that, I would generate a table containing Temperature & corresponding Enthalpy columns referring to Property chart of R134a refrigerant .

For instance, lets say I create a table with temp.values with every 10 degree step-

Temp.       Enthalpy

  :

-10               100

0                  200

10                300

20                400 

30                500

:

: 

But what if my temp.falls somewhere in between 10 to 20 ; some intermediate value like 15.7 or something?

For this reason, I need to do some interpolation which will calculate corresponding Enthalpy values for such intermediate value.

How to do this? 

There is a VI called "Interpolate 1D" in the functions pallette, but I am unable to understand how it functions.

Kindly educate me in this regard. I am using LabVIEW 8.2.1 Kindly post your suggestions by saving your VIs in this version.

Thanks in advance.

-Snehal Upadhye

CLAD

[GerdW]

Hi Snehal,

as a CLAD you should know all this:

As the snippet tool of LV2013 mangles the blockdiagram (by replacing the array constant by a control and a scalar constant) I attach a real picture too:

[tst]

---

@GerdW wrote:

As the snippet tool of LV2013 mangles the blockdiagram

---

The snippets made by the code capture tool don't have these issues, in case this really bothers you. You can install the CCT from VIPM. Just saying.

[SuLAB]

Thank you GerdW.

Though I am CLAD I have never come across any such application which would require some kind of interpolation; hence it is not necessary that every CLAD should possess knowledge about everything in labview.

Now , I have another question- How to write a table with below mentioned format in labview i.e with merged cells.

I know how to write a table in labview; but not able to write in the same format that is given below.

I want all my four enthalpy columns merged under a same column "Enthalpies(KJ/Kg)". How to do it?

Sr.No.	Suction Pressure(Bar)	Saturation Temp	DischargePressure	Saturation Temp	Enthalpies(KJ/kg)				Density at T3
	P1	ts1	P2	ts2	H1	H2	H3	H4
1
2
3
4

Thanks & Regards,

Snehal Upadhye

CLAD

[GerdW]

Hi Snehal,

are you talking about a table indicator on a LabVIEW frontpanel or about a "table" aka Excel spreadsheet?

Table indicators do not allow merged cells...

AFAIK Array interpolation functions are also asked for in the CLAD exams. As a CLAD you should have (atleast) the knowledge to know where you have to look for appropriate functions...

[SuLAB]

Hello GerdW,

Thanks for reply.

I need a table indicator on labview front panel in given format.

I have already written it to excel spreadsheet; but my front panel table indicator also should appear like the table I have shown.

For any exam everybody prepare in their own way so its just might be that I havn't come across any problem regarding array interpolation; though I already knew that there is a function called interpolate 1d array and where it is located!!! 

Thanks & Regards

Snehal Upadhye

CLAD

[SuLAB]

Hello,

Is there any function which would give interpolated output from combination of two inputs?

My first problem was solved with Interpolate 1D array function; Now I need to obtain enthalpy values from combination of temperature & pressure inputs.

I have total three columns for eg. ----

Pressure              Temp.           Enthalpy

1                           10                  100

2                           20                  200

3                           30                  300

I want LabVIEW to give me enthalpy values considering "both" the temp.and pressure readings.

Kindly suggest me some solutions. Thanks in advance.

Best Regards,

Snehal Upadhye

[GerdW]

Hi Snehal,

LabVIEW also has functions to do 2D interpolation...

[SuLAB]

Hello GerdW,

Thanks for reply.

Before writing this post ; I have already tried using "Interpolate 2D" function with method "Bilinear" but the results were not as expected.

I think I am missing something somewhere that I am not able to identify.

Could you please give an idea which would help me finding my loopholes?

Thanks & Regards,

Snehal Upadhye

CLAD

[udka]

Hi Sneha,
Can you explain what was expected and what you got. may be post vi/screenshot if possible will give better idea.