Humidity and Temperature transmitter

I'm very new to the plc game. My newest experiement is to wire up the Omega hx93 humidity and temperature transmitter to my slc 5/03 processor 7 card rack with a thermocouple input card 1746-nt4. I see here it has four channels im guessing i only need one of them and then i have to power up the omega hx93 ?

Greetings H2wall and welcome to the forum.



According to the manual http://www.omega.com/manuals/manualpdf/M0933A.pdf the transmitter has two 4-20mA outputs, one for temperature and one for RH, therefore you would need a milliamp input card, not a thermocouple input card, something like the 1746-NI4 or 1746-NI8, and you will need to use two channels on the card.

Once you have the correct card and have it wired and configured correctly as part of your program IO you will then need to scale the analog inputs to give you a number that matches real world units, or what we call engineering units. In this case that is degrees C and percent relative humidity. The analog input cards will return the raw A/D conversion, that means a number between 0 and 32768. It is easiest to use the SCP instruction to do this.

Looking in the manual for the 1746-NI4 we can see that it returns a value of 3277 at 4mA and 16384 at 20mA. Looking in the manual for the transmitter, we can see that it operates in a temperature range of -20 to 70C and an RH range of 0-100%.

If for example the -NI4 card was in slot 6 and temperature was wired to input 0 and RH to input 1, then

SCP I:6.0 3277 16384 -20 70 N7:0 will put the temperature in register N7:0.

and

SCP I:6.1 3277 16384 0 100 N7:1 will put the relative humidity in register N7:1

Now you can use registers N7:0 and N7:1 as needed elsewhere in your program.

thank you so much that couldn't have been easier explained and it teaches me how to find an interpret information too and how much you can do with a plc and how configurable they are.