Measuring flow with Siemens S7-300

[gigacer]

Hi, i am beginner with a PLC Systems and i have a couple of questions about flow measuring with a Siemens S7-300 PLC. I need to measure flow in the pipe with a sensor on the picture.

This sensor on the picture is RS Stock No. 256-225 ( here are the specifications ).

This sensor was previously connected to a ''Frequency to voltage converter'' and than from there the value of the sensor was displayed on the digital LED display. Frequency to voltage converter uses the LM 2917 ( here are the specifications of the LM2917 ) and the shema of the frequency to voltage converter is shown on the picture below.

I need this sensor connect to a PLC, so here are my questions:
-can i connect this sensor directly to a Siemens S7-300 PLC (on which module)?
-if i can't connect it directly, can i than use this frequency to voltage converter to connect this sensor to a Siemens S7-300 PLC (on which module)?

 

[osmanmom]

Lab or Industries application?

 

[boneless]

Yes, there are several compact CPU's that have built in pulse measurement (I use the 313C a lot). There are also specialized pulse measurement modules, the are under the FM-300 tab. My Siemens Mall seems to be down at the moment, but if you have a single signal FM 350-1 is what you need, FM 350-2 has up to 8 channels. Note that these modules are pretty pricey, depending on your application a pulse-to-analog converter might be much cheaper. Something like this:

http://www.turck-usa.com/illustrations/B4400_C25-C26.pdf

 

[gigacer]

this is a Lab application (school project), i have a CPU 314 IFM, this CPU can measure frequency up to 10 KHz, can i use this CPU? which SFC block should i use in Step 7 for the frequency measurement? does anyone have some useful links that could help me with this? i didn't find much stuff on the internet

 

[boneless]

What is the order number for the CPU?

Standard manual here:
https://cache.automation.siemens.com/dnl/TA1NDkxOQAA_15390415_HB/S7-300_IHB_e.pdf

Special Functions:
https://support.automation.siemens....lib.csFetch&nodeid=1135541&forcedownload=true

 

[gigacer]

thanks, order number: 314-5AE10-0AB0

 

[gigacer]

hi, again me, i have read in ''Programmable Controller
Integrated Functions CPU 312 IFM/314 IFM'' manual that i must use SFB 30 block to measure frequency. This block has possibilities (if i figured out it correctly) to set upper and lower comparison value for frequency so PLC can than for example light up a red bulb if the frequency is too high or too low. i don't need such features, i just need to read a frequency value from my flow sensor, so could somebody explain me following:
- do i have to set this upper and low values?
- will SFB 30 give FREQ output if i dont do that ?

Picture of SFB 30 block

 

[boneless]

I believe you do not have to set this, and I believe it will work without it. In any case you can input values outside of your range.

Just give it a try. Trial and error are the best way to learn (as long as it is safe )

 

[mk42]

Besides trial and error, the help file is a great way to learn as well. Click on the block, then hit F1. It should jump you straight to the help for the block.

 

[gigacer]

hi, i wan't to try it, but i am not sure how to connect this sensor to CPU 314 IFM, i know that this CPU has 4 special inputs ( I126.0 - I126.3) and i know that i can use one of them for frequency signal (meter), but i am not sure how to wire supply voltage and ground, in the Siemens manual there is this example of the wiring BERO sensor to CPU 312 IFM (special input I124.6) but it didn't help me, can someone draw me on this picture how to wire this sensor to CPU 314 IFM

 

[danw]

I don't know whether my wiring will work or not, but here's the terminal designation I found for the 314 IFM and the statement about 126.0 through 126.3 digital inputs being used as frequency inputs.

In the process world, people do not usually use analog input card or CPU DC power terminals, L1+ (DC power) and M (DC ground), for powering field instruments. They usually use a stand-alone DC power supply.

I'm sure there are limits to how many mA or amps L1+ can supply and I don't know what that limit is, but you might research it, or just use a regulated 24Vdc power supply.

 

[gigacer]

thank you, i will try it that way