Add the capability to express limits in +/-% of expected value in all limits

[jeffh12345]

Almost all of our analog measurements are specified in %: example

a Power Supply DMM measurement limit is 24.00Vdc +/- 5%

We typically have 100+ measurements like this in a project

Why not include it in the default step types as an optional selection?

I sure would use it, so would my team.

I agree that it should not alter existing programs using the default step, but I believe that this feature should have been in Teststand when it was first released.

I have run across this in both analog measurements, and the results from an ADC

Think a limit of 0x234 +3%, -7%

[PhillipBrooks]

Excellent idea! I believe this would require the addition of a nominal value property for a limit.

I am suprised that the TestStand help returns nothing when you search for the word nominal.

I worked in a metrology lab some years ago; a nominal value combined with % or PPM was the standard notation used in defining limits. I wrote all my code at that time in LabVIEW, but TestStand certainly would have been easier to use if a nominal value concept existed.

[Dennis_Knutson]

This is actually easy to implement if you have any experience in writing custom test steps. You can create a new numeric limit test with a modified edit step. I did this where you could specify a UL and LL as a percentage. The step then calculated the absolute UL and LL and wrote those values to the standard limits container. I agree that this would be nice to have as a standard feature, though.

[j_dodek]

I have also implented this in my step types

This should be a standart feature!  If i am doing numeric limit there is most times +/- %

Very goog Idea!

Juergen

[Jervin Justin]

Dennis / Juergen,

As a stop-gap, would you be willing to post this as an example on the NI Community page?

Thanks,

Jervin Justin

[StephenGerads]

Currently, it is easy to use expressions to implement % limits.

For 24+-5%:

24 * 0.95

24 * 1.05

or in some cases:

Locals.NominalVoltage * 0.95

Locals.NominalVoltage * 1.05

[dug9000]

Just want to clarify this idea a bit. Is this primarily a use case where you have a single expected/nominal value and you want to specify the upper and lower bounds as a percentage of that value, or would you sometimes also already have an upper and lower limit and want to specify a tolerance percentage for those limits.

For example, do you want the following:

A limit test where the upper limit is 20 with a tolerance of 10% (i.e. really the upper limit is then 22) and the lower limit is 10 with a tolerance of 10% (i.e. really the lower limit is then 9).

Just want to clarify whether this is a per-limit thing that applies to all comparison types or really just a new kind of comparison type that specifically addresses the single expected value with upper/lower limit expressed as a percent of that value.

Thanks for any insight on this.

[Elaine_R.]

dug9000,  I would imagine this would be just a different flavor of Numeric Limit Steptype... at the end of the day it would still evaluate as a GELE (or perhaps we need to have user specify whether it's GTLT / GELT / GTLE ? Scary thought... )  I suppose we could stretch and say that it could apply to ALL comparison types, but I've never seen a usecase where the % was single ended... I could be proven wrong! I suspect that 99% of usecases however would be GELE.

The 'ideal feature' would be the simplified edit interface with only center and offset% instead of requiring user to calculate and adjust the UL and LL/ or type in expressions... currently I just type in the expressions when I get requirements like this, but they do look ugly...

it's such a cosmetic thing that I'm torn as to whether it deserves to be it's own step type or not... maybe just a new checkbox / boolean step property on numeric limit steps where you choose how to specify limit and use an alternate limit storage container to hold the different data? then apply an alternate status check string in event the user has opted for % based range checking?