1756-of8 question

I have the card setup for the following
0-20 ma on the channel
low sigal =4ma
high signal = 20 ma
low eng = 0
high eng = 100

Now I am expecting that when I send 100 to the ch0Data tag for the card that I should see 20ma. The most I see is 5.6ma. If I go thru the calibration routine everything works properly, 4ma on the low and 20 ma on the high. What am I missing?

The problem is likely on the Limits tab, where the default value for High Clamp is 10 and for Low Clamp is -10. They don't change automatically when you change the Engineering Units.

If the output is clamped at 10 Engineering Units, that's consistent with the output being 4mA + (0.1 x 16 mA) = 5.6 mA.

duh!

Thanks Ken! I think I can speak for most everyone when I say that it is great having you as a resource on the forum. Appreciate you help on this.

I'd like to have a Nickel for every hour that has been lost by programmers due to the default values for this analog output configuration parameter. It seems redundant to me to even have these limits as a configuration option. I've been limiting analog output values for decades without having this option at the hardware configuration level.

This is a topic I cover in my classes, don't beat yourself up on this, nearly everyone misses that "Limits" tab.

I've seen many an experienced commissioning guy hung up on this. I've even seen new control valves ordered, because the ones they have "don't work". (I guess they forgot to actually measure the 4-20mA output !!)

As Ken stated, the limits (clamps) do not "track" your configuration of engineering units, which is a shame. IMHO the default limit values should update to "max+" and "max-", meaning they don't come into play until you change them.

daba_logic.....

MaxLimit := MaxEU
IF UserSet_MaxLimit < MaxEU THEN MaxLimit := UserSet_MaxLimit

similar for MinLimit ...