Error Reading a negative value with Read Input S16 (4)

[cdelareza]

Well I'm reading a metering value that is expected to be sometimes negative, I'm using Read Input S16 (4) to do so, and the value I'm reading is ie.

-31954

should be:

-814

or

-31942

should be

-826

I've made some calculations and found that if I subtract a constant value of

-32768

I get the value I was expecting.

So I wrote the event of my channel

IF(L1_734_P<0)

VAR.MED=(-32768)-L1_734_P

ELSE

VER.MED=L1_734_P

ENDIF

I was trying to use a CONVERSION but it does seem that I can't use IF in my FORMULA.

Anyways let me know if what I'm doing is ok or I'm doing something wrong in the I/O type of my channel.

Thanks

[AzeoTech]

Hmm, sounds like your device uses a non-standard integer format.

Anyhow, you can use an inline if to do what you need in a conversion:

iif(Value < 0, -32768-Value, Value)

[cdelareza]

Thanks the inline "if" works just fine, however I've changed the IO Type to Read Input S32 R Words (4) and it seems to be working ok.

I will ask the device manufacturer about it's comm standards and let you know.

thanks again.

[AzeoTech]

Are your values actually 32 bit values (i.e. use two registers)? If not, then you probably just got lucky that it worked, likely because the negative bit got moved into a different register that happened to be 0. It will likely stop working when the adjacent register changes value. Just because it worked now doesn't mean its right.