SIEMENS CPU314 IFM How to Read resistance

[NiCeBoY]

Hi,
I am using a Siemens CPU 314IFM with
DI4xDC24V | AI4/AO1x12Bit module.

I want to know the position of a motor by coupling a 10k Ohm resistor with it.
The system is already setup like that.

It a manual valve connected to a small DC motor coupled with a Variable resistor.

I need to determine if the valve is open or close by reading the value of the resistance of the potentiometer.

Anyone can help me how to wire the potentiometer with the PLC and configure?

Below are some images of the plc I/O and the valve/motor/potentiometer setup.

PLC I/O

Valve

Valve

Thanks

 

[JesperMP]

On the 314IFM you have +/-10V and +/-20mA analog inputs available, no resistance inputs.
So you need an external converter to change the 0-10kOhm to either volt or current, or add a resistance analog input module to the 314IFM.
Here are the technical specifications:
http://support.automation.siemens.com/WW/view/en/8860591
On page 1-59 you find how to wire up the analog inputs.

N.B, that 314IFM is quite old by now.

 

[NiCeBoY]

How about if i run a voltage through the resistor and measure the voltage drop? or current?

 

[KalleOlsen]

How about if i run a voltage through the resistor and measure the voltage drop? or current?

Yes, it is a common solution. 10V over the pot, measure voltage between 0V and the 'glider'.

Kalle

 

[sthompson]

How about if i run a voltage through the resistor and measure the voltage drop? or current?

You might be able to do it with 0-10 VDC, it depends how much accuracy you need. You will need a Linear Taper Pot. Connect 0VDC (Common) and 10 VDC (Supply) to the ends of the Pot, and run the Common and Wiper Arm to your Analog Input Card. As with all Voltage Divider setups, there will be an Error caused by the Series/Parallel arrangement with the Analog Input. However, if the Analog Input Impedance is high enough, it should be negligible.

Stu....

 

[NiCeBoY]

Hope the resistor will not heat too much.
i'll give it a go in the next coming hours.

 

[sthompson]

Hope the resistor will not heat too much.
i'll give it a go in the next coming hours.

Kalle types faster than me, and said basically the same thing in fewer words.

P=E*E/R or Power equals Voltage Squared divided by Resistance.

So ignoring the parallel resistance of the Analog Input.

P=10X10/10000 = 0.01W

Stu....

 

[NiCeBoY]

Cool i did this connection but i am using 9V supplied to it. I dont think that will be a problem.
I am using 9 V because i can only get a Voltage regulator IC for 12V or 9V. So i choosed the 9V.

Tomorrow i'll try to read it from my PLC on the software simatic manager.

What function i can use in the program to read the analog input?

Also is there any setting i need to setup for the I/O?

Cheers

 

[iant]

hello NiCeBoY
DKSH in Hampton park onsell the adjustable ADLM power supplies - a 12V range but you can do it better than than PM your Email
I am LOCAL to YOU - near casey central

 

[NiCeBoY]

Power supply is not a problem, i just want to use less stuff..
anyways around how much they are?
cheers

 

[JesperMP]

How is adding yet anot power supply simpler than adding a resistance converter ?

If you want it to be REALLY simple, just add a 15 or 20 kOhm in series with the pot, and connect everything with the regular 24V powersupply as you use for the CPU.
Resistor and pot will act as voltage divider so you get approx 10 V over the pot.
It wont be super accurate, but I think it doesnt matter for your application.

If you are regulating water flow, then I think you have a bigger problem with that the valve will not work in a linear way.

 

[NiCeBoY]

yeh coool...
once i do that, what is there any configuration thats need to be done in simatic manager? also what function i can use to read the input of the analog module?

MUL_I ??

cheers

 

[JesperMP]

Look in the HW Configuration for the PIW adress that contains the analog value.
To scale to an engineering value, you can use FC125 SCALE from the standard library.

 

[NiCeBoY]

ok cool.
i'll try to find where FC125 SCALE from the standard library is tomorrow once am @ uni.

Cheers mate