Analogue inputs

Hi

its been a while since I did any plc programming & things have moved on somwhat Im looking for some programming examples for the mitsi alpha specifically using analogue input from a humidity controler with 0 - 10v Im struggling to understand the scaling or gain function or what figure I need to represent a 0 - 10v range
any example would be appreciated.
the aim is to control some heaters in relation to the humidity
for crop drying purposes

Pactrol

For any unit conversion on any PLC you can use four function math with the following, which asumes integer math:

DataOffset = Data in input register at 4 mA (or zero analog signal of whatever range - for example 0 VDC on a 0-10 VDC transmitter)

DataSPan = Data at 20 mA - Data @ 4 mA

FACTOR = arbitrary factor (multiple of 10) needed to get proper resolution and accuracy

EU = Engineering Units x FACTOR

EUOffset = Engineering Units @ 4 mA x FACTOR

EUSpan = (Engineering Units @ 20 mA - Engineering
Units @ 4 mA) x FACTOR

DATA = Actual data reading in input register

EU = ((EUSpan x (DATA - DataOffset))/DataSpan) + EUOffset

ProcessValue = EU / FACTOR

For Example, 0-60 psig from 4-20 mA with resolution of 0.1 psig:

FACTOR = 10
Data @ 4 mA = 6240
Data @ 20 mA = 31208
DataOffset = 6240
DataSpan = 31208 - 6240 = 24968
EUOffset = 0 x 10 = 0
EUSpan = (60 - 0) x 10 = 600

DATA = 18975

EU = ((600 x (18975 - 6240)) / 24968) + 0 = 306

Process Value = 306 / 10 = 30.6 psig

Hi

yes Ive been reading some of the posts from what I understand with 4 - 20 ma you have to offset by 6240 but your range appears to be all positive
where as on the alpha Ive a range of -65536.0 to 65536,0 so where would zero volts be its the negative integers Im not understanding
I would probly understand it better if I had an example to compare with unfortunately mitsi dont produce one Ive searched their sites
so I may have to look at some other brand preferably one that provides
some program examples to study.

pactrol

Hi

generally the analog would only go negative if the process went negative, this may be a speed feedback from an inverter drive running in reverse, for example.

If the process transducer is 0-10V then the PLC counts would be 0 to the max resolution of the particular PLC.

Hope this helps

Hi

So 0 volts would be 0 & 10 volts = 65536.0
& to scale this from 0 to 100 I divide 65536.0 by 100
is that correct

Pactrol

The formula is universal. For Example, 0-100% RH from 0-10 VDC with resolution of 0.1%:

FACTOR = 10
Data @ 0 VDC = 0
Data @ 10 VDC = 65536
DataOffset = 0
DataSpan = 65536 - 0 = 65536
EUOffset = 0 x 10 = 0
EUSpan = (100 - 0) x 10 = 1000

DATA = 18975

EU = ((1000 x (18975 - 0)) / 65536) + 0 = 289 (assumes result is truncated)

Process Value = 289 / 10 = 28.9 % Relative Humidity

right I think Ive got it

data input 18975 / 65536 =0.289 x 1000 =289 / 10 = 28.9% RH
thats near enough for me
thanks

Can someone please explain what the

"DATA = Actual data reading in input register"

Is in a little more information