Question on A/D inputs

[rossw]

A/D channel 1, 2 and 3 are nominally 0-10V input, and thats fine.
A/D channel 4 is "reserved" for the humidity sensor - however is it possible to access the raw value (0-1023) directly?
If so, is there anyhing actually "special" about its signal conditioning, or is it purely a software fudge to linearise it to the humidity sensor?
If its all just software trickery - can I actually use it as a 4th A/D input, and what is its nominal input voltage span?

 

[rossw]

Just to clarify.... I know if I retrieve all variables via XML I see what appears to be all the raw values:

<aip1>3</aip1>
<aip2>3</aip2>
<aip3>2</aip3>
<aip4>1</aip4>
<aip5></aip5>
<aip6></aip6>
<aip7></aip7>
<aip8></aip8>

however in PLC code:

set var1 aip1
set var2 aip2
set var3 aip3
set var4 aip4 <-- this is rejected.

 

[fwd03]

I asked this question to the support before. I remember they told me that the aip4 is actually hard coded with humidity sensor calibration curve logic.

 

[CAI_Support]

That is correct. humidity sensor hardware directly goes to a logic based on calibration data from the Honeywell humidity sensor.

 

[rossw]

That is correct. humidity sensor hardware directly goes to a logic based on calibration data from the Honeywell humidity sensor.

It hasn't answered my question though.
The XML output includes both humidity (percent) as well as AIP4 (as a count). So the raw count data is *available* to the engine, somehow.
Why can't I access the raw number in the PLC code?

 

[CAI_Support]

The analog input for humidity sensor is directly calculated and stored as humidity. All the I/O is not only taken when checked in PLC, they are on scheduler.

 

[CAI_Support]

We could add a variable to let you use AIP4 raw value in your PLC. But remember that input is not over-voltage protected and it also has resistor network in front to divide the 5V output to fit 3.3V input. You may have to modify the hardware to bypass the resistor network.

 

[rossw]

We could add a variable to let you use AIP4 raw value in your PLC. But remember that input is not over-voltage protected and it also has resistor network in front to divide the 5V output to fit 3.3V input. You may have to modify the hardware to bypass the resistor network.

That would be fine. You already return AIP4 in the XML results, so its just letting it be used as an operand in the PLC code.
No overvoltage protection is fine because it will be driven from an opamp, I can easily clamp its output.

 

[CAI_Support]

Ok, we will make this change and let you have it