Analog inputs in RSlogix500

Hi
I am new to this forum. I need help regarding RSlogix500 Analog input card programming.
We are using 1746-NI16I .16 analog inputs. I need to convert 4-20mA input to operate a Mass flow valve so there is an analog output also to the valve.
i totally have no experience in RSlogix since i have worked with siemens and Ge fanuc. This is also m y new job.
help me regarding this
{4-20mA) ---> (analog input card) -----> (0-100% open valve)
rgds
chitra

A little more info would help someone help you.

Do you want to control flow with a PID control? Have it control at a predetermined setpoint?

What does the 4-20ma represent in engineering units?

Do you have an analog output card,if so give complete catalog number?

And what PLC do you have, complete catalog number?

And welcome to the forum.

Hi
Thanks for replying so quickly.my card details are as follows
1746-NI16I,1746-N08I, 1746-L551 cpu.Have it controlled at a predetermined setpoint.

I need another help.
I have a compressor and to check whether the compressor is working i have a pressure transmitter (ie, once the compressor is ON,the pressure in the line should increase,if not the compressor fault signal should be given ).What instruction to use tocheck whether the pressure transmitter value is increasing?The PLC is Allen Bradley SLC500. RSlogix 500 S/W

Thanks
chitra

See link below for a place to start your PID learning.

http://www.plctalk.net/qanda/showpost.php?p=468570&postcount=4

Have you installed these cards yet, if so can you post your .RSS file ( zip it first). Or tell us which slot they are in.

What instruction to use tocheck whether the pressure transmitter value is increasing?

Click to expand...

"Compare" (CMP). Previuos value to new value.

What instruction to use to check whether the pressure transmitter value is increasing?

Click to expand...

As Mickey said, use one of the comparison instructions, such as GRT (Greater Than). GRT compares the Source A value to Source B value. If true, the GRT output goes true.

Chitra, you did not answer this question:

What does the 4-20ma represent in engineering units?

Click to expand...

If Mickey knew what units of measurement your signal should mean(minimum and maximum values), he could set up the SCP scaling instruction for you. Yes, you will have to know those units and values to get the correct mass flow number into your PLC program.

Hi
Sorry i forgot to tell you it is 4 to 20 milliAmperes current input.
What is the corresponding value in RSlogix (is it 0-32767) ? Also i want to know how to program the analog output. A sample program would be very helpful.
Thanks
chitra

This is a confusing part of SLC programming, and I often find programs running with incorrect scaling where people have made a mistake with it.


I always set my analogs to RAW/Proportional in the configuration, so you maximise the resolution. In this mode, the following scaling applies.
Analog Inputs scaled 4-20mA = 3277 to 16383
Analog Outputs scaled 4-20mA = 6242 to 31208.


The 1746-NI16I can be configured in different modes, class 1 or class 3. Class 3 allows detailed configuration changes, where class 1 is just raw 0-20mA= 0-16383.

When passing to and from a PID loop, I normally scale 0 to 16383 as this maximises the resolution of the PID control.
So scale your analog input and your setpoint to the PID range.
The output then needs to be scaled from 0-16383 to the analog output range 6242-31208.


You also have the option of configuring the input and output modules "scaled for PID" which then scales them all 0-16383.
Modules may also be configured as engineering units which would be 4000-20000 for 4-20mA. This is personal preference which way you do it.


This is all very confusing at first, but you get used to it.
With all this in mind, best read the manual. All this info is from memory, as I have these numbers burnt into my brain.

A sample program would be very helpful.

Click to expand...

Here are two samples with old-style scaling Compute instructions. This illustrates the mathematics. Now you would probably use SCP with the hidden math to solve the scaling equations.

Notice that to scale the input, you first need to know the expected flow range in engineering units (0 to 132 gallons per hour).

Lancie1 said:

Here are two samples with old-style scaling Compute instructions. This illustrates the mathematics. Now you would probably use SCP with the hidden math to solve the scaling equations.

Notice that to scale the input, you first need to know the expected flow range in engineering units (0 to 132 gallons per hour).

Click to expand...

Hi,
Thanks for the sample pgm. I could get an idea now.
I would come back incase i mess up with the scalling. As FATcontroller has replied i have started to read the manual now. It is very useful. A big thanks to him.
Now...
My management told me to select HMI panel of my choice(but should be good one) to interface nwith this ALLenBradley PLC. I suggested on using HAKKO Panels since i have experience with using it ( in my last job i used it with GeFanuc PLC.) Is it OK ? Does anyone have experince with SLC500 and HAkko panels ?