Absolute Value

[Clint Eastwood]

Couple questions:

I'm using a LV Prototype adapter to measure resistance ( PXI4071) in Teststand.  I then store this value in a local variable (locals.R2). I all ready have a local variable created w locals.R1 stored in it which is my baseline.  My reqiuement is to verify locals.r2-locals.r1 < 5 ohms.  If not fail the test.  I'm doing all this in 3 steps.  Seems to me I can do it all in at least 2. 

Current:

1) Measure the DMM ( Labview)

2) statement step f(x): locals.result=locals.r2-locals.r1

3) none adapter using a Numeric Limit test:  check locals.result<5 which gives me the pass/fail criteria.

Any way to combine steps 2 and 3?? Couldn't find anything on the web or in the old manuals.  I guess "Step.result.passfail" no longer exsists?

Also, when I use abs(locals.result)=locals.r2-locals.r1 and watch locals.result after the step is exec I get zero.  If I take out the abs it does the subtraction, ie I get a value.  Why??  What is wrong w that statement/formula???

Thanks,

Clint

[Captain_Jack]

Clint,

You can add the step 2 (f(x)) step to the Pre-Expression of step 3 to do it in 2 steps.

If you want to do it all in one step, then change the measure step (1) to a Numeric Limit step type with the settings from step 3 and add the statement in step 2 to the Post-Expression of that step.

Why your watch window doesn't work I don't know. It works OK on my system when I pasted in what you wrote.

-Jack

[Snowman 6008]

Clint,

When you use abs(locals.result)=locals.r2-locals.r1 you are setting the value of the absolute value of locals.result to be equal to r2 - r1, and not the actual value itself.  If you used the expression (Locals.result + 2) = 5 you would also recieve a value of 0 for Locals.result because you are not assigning a value directly to Locals.result. Even if TestStand were to evaluate the algebraic expression for you, then in abs(locals.result)=locals.r2-locals.r1 the value of locals.result would evaluate to be equal to plus or minus (r2 - r1); see: Solving Absolute Value Equations .If you want to store the absolute value of r2-r1 in locals.result then the expression would need to be written as locals.result=abs(locals.r2-locals.r1) .

[Clint Eastwood]

Thanks Richard.  After my 1st post "Dawn broke over Marblehead" and I had already tried the abs around the r1-r2.  Now you've provided an explanation as to why it worked.

Clint