fahrenheit to Celsius Unit dsplay LV 8.2.0

[richjoh]

yea, I know its easy, I didn't want 4 controls on the FP. I could hide the one not in use and put them back on FP.

My point though is still valid. Since temperature does not convert linearly with the other units you have to do convert from Kelvin all the time. This is unlike say using one control on FP and converting from m to ft, in, mm, ... whatever. The unit allow the user to make the change. With temperature, if I want to do the same conversion from Kelvin is needed...

richjoh

[GerdW]

Hi richjoh,

you simply should use "degF" - or even better (from my continental European view) stick with SI units

When you want to calc/display temperatures you should use the correct units, being "K", "degC" and "degF".
Only when you need temperature differences you should use "Fdeg" and "Cdeg" (in physics I learned always to use Kelvin for temperature differences, just to mention SI units again ).

IMHO I like "°C" more than "degC", so on my vis I never use the unit display for temperatures...

[tbob]

Here is a slighlty better vi that has one control, one indicator, and one enum.  When a user wants to convert, you can have a pushbutton that selects the type of conversion, and then call this vi with the correct enum input.

[richjoh]

Thanks for all the converters, but I don't need any now that I found the problem. NI documentation has a typo error here, I been duped! Whats labelled relative is absolute and whats absolute is labelled relative. Its easy to remember the difference. Absolute temperatures start from zero (0) degree and go positive. Relative temps reference a zero point (say freezing water 0 deg C) and are negative below this and positive above.

Thus. NI please correct the post showing the temperature scale... I'll repost the link here from the top of the thread http://zone.ni.com/reference/en-XX/help/371361B-01/lvhowto/available_units_in_labview/ . All this time I been using Fdeg and Cdeg and its not the relative degrees

Now if I use the degC and degF everything works out just fine, no conversion needed since these are the relative conversion. Once again the NI document say they (degF and degC) are the absolute... this is a typo on NI part.

best regards,
richjoh

[RavensFan]

I agree with you that the documentation is confusing and needs to be fixed or clarified.  But I think the real problem is why did someone come up with Cdeg meaning the same as Kelvin, which looks a lot like degC but does not mean the same.?  If someone wants to use the SI scale for temperature based on absolute 0, then the units should be Kelvin.  If someone wants to use the traditional Fahrenheit scale based on absolute 0, then the units should be Rankine  (which doesn't even show up on that list.)  In no way should the units of Cdeg nor Fdeg be used in anyway to imply a temperature scale based on absolute zero and LabVIEW should be fixed.  Of course that would break code anyone as already written to work around these issues.

[Rod42]

Perhaps the documention could user better wording, but I would say that it is correct.

In Kelvin and Celcius a change of 1 degree is the same, and is a bigger change than a change of 1 degree on the Farenheit scale. There are also offsets between them all, so unlike other measurements, zero is different on all three scales. (We don't have 0 metres = 32 feet)

I agree with GerdW's interpretation; maybe an expansion on his explanation would help

Relative temperatures refer to DIFFERENCES in temperature. If a temperature changes by 40 degrees on the Celcius scale (40 Cdeg) it will have changed by 72 degrees on the Farenheit scale (72Fdeg). Thus 40Cdeg = 72Fdeg.

The "absolute" temperatures are those a thermometer would register. Here 40degC = 104degF

As you now have differences available you can add, so 40degC + 40 Cdeg = 176degF.

So it's meaningful to convert between Fdeg and Cdeg, also between degC and degF but not between the two groups.

If you have a change in temperature, you should add or subtract Cdeg or Fdeg to the start temperature in degC or degF.

As all calculations are make internally in K, you can use K anywhere, and convert K to either of the pairs of units, remembering that between K and degC or degF you are converting temperature that would be shown on a thermometer, and when you are converting between K and Cdeg or Fdeg you are converting the change on temperature. It follows therefore that the numbers shown by Cdeg and K are the same.

Rod.

Message Edited by Rod on 03-05-2008 01:54 PM

[JB]

You might be interested in this tutorial thats shows how to implement a dual mode thermometer with an XControl. This exactly example ships with LV (search "XControl" in the NI Example finder).

[richjoh]

Rod,

I already explained how to distinguish Relative temperature... did you not read my thread above??? Your definition of Relative temperature is meaningless since all temps readings have some "relative" difference. Why not KISS. As I read your post more its add confusion...

JB,

the xcontrol is overkill for what I'd like to do. My soln is just show the unit during runtime and user can select the preferred temperature. On my block diagram I convert the unit to a regular number and input this to my setting of the temperature...

richjoh

[JB]

Yes I agree. However, some people may be interested to know that a ready-to-run example ships with LV.

[RavensFan]

---

Rod wrote:

.

The "absolute" temperatures are those a thermometer would register. Here 40degC = 104degF

As you now have differences available you can add, so 40degC + 40 Cdeg = 176degF.

So it's meaningful to convert between Fdeg and Cdeg, also between degC and degF but not between the two groups.

If you have a change in temperature, you should add or subtract Cdeg or Fdeg to the start temperature in degC or degF.

As all calculations are make internally in K, you can use K anywhere, and convert K to either of the pairs of units, remembering that between K and degC or degF you are converting temperature that would be shown on a thermometer, and when you are converting between K and Cdeg or Fdeg you are converting the change on temperature. It follows therefore that the numbers shown by Cdeg and K are the same.

Rod.

---

True, but as Ricjoh as just said as well.  40degC + 40 degC also equals 80 degC which equals 176 degF.

40deg C + 40 K also equals 80 degC.

The use of Cdeg and Fdeg is just unnecessarily confusing with degC and degF, when the units should actually be K and R  (and where is R?????):smileywink: