Load Cell for Siemens PLC interface

ming0521

Member
M
Join Date
Dec 2011
Location
Ohio
Posts
8
I'm currently working on my 'Weight Sorting PLC Trainer' for my thesis.

I am using a thin beam force sensor to determine the weight of my object. Now I want the signal sent to my PLC S7-200 module. I am just going to weigh small objects.

What should I do? Thanks!

Best regards!
 
Most likely, you will need some sort of interface for your load cell. Generally, a load cell will require an excitation voltage and will produce a millivolt signal. mV cards for a PLC can be expensive, and may not be able to supply the excitation voltage. So, if it were me, i would look for a signal conditioner which is compatible with the load cell and can generate an analog signal for your PLC that can be read via a standard type of analog input.

My knowledge of siemens PLCs is very limited, so I will defer to others to give you more specific information.
 
Since you are using a S7-200 the easiest way would be to use a SIWAREX MS weight module that connects directly to your S7-200.

Part#
7MH493000AA01

How are you planning on displaying your weight data?
 
nonuke, what does the PR2261 cost ?
Didnt even know it existed. Its existence is pretty well hidden on PR electronics website.
It could be an OK transmitter for simple single loadcell applications.
 
One thing to rememeber when using a signal conditioning device. You will lose resolution. Depending on the bit resolution of the analog input of the PLC and the bit resolution of the analog output from your transmitter this can be significant.
 
JesperMP:
The price for one unit ias about 200€.
But in my next application, I'm going to try the model JOLLYTB with a cost of about 120€ or the profibus model JOLLYTBPROFI for about 200€
The supplier is: www.laumas.it
 
Thanks nonuke.

Looks interesting. I like that it has a dedicated input per loadcell for up to 4 loadcells.
I tried once a loadcell transmitter from swedish Vetek (http://www.vetek.se/Vagtransmitter-4-kanaler-Ut-RS232485-4-20-mA/article), but it was actually manufactured in italy. Worked OK but the setup was really very quirky with a poor manual. Hope it is not the same italian company ;)

May try to see if that JOLLYTB is something for me. The price is incredible. Be sure to post your experience with it.
 
load cell to PLC

hi i interface a loadcell to a pic processor but never to a PLC you need a signal conditioner that makes mV/volts or mV/4-20ma and then do the proper calculate in you program for the signal readed.
Loadcell specification: 2mV/V/300kg means that if you use 10V excitation, you get (10V x 2mV/V) = 20mV full scale output for 300kg.
If you have a loadcell 2mV/V/5kg & you use 5V excitation, the linear equation will be 10mV for 5kg.
 
nonuke, I think that the last device you linked to requires an external summing box, or am I wrong ?
I really hate the summing boxes. A dedicated input per loadcell is much better. And I usually only need 3 load cells. 4 would be the odd case. Never more than 4.
That is why I find the JOLLYTB interesting.
 
Little off Topic

JesperMP said:
nonuke, I think that the last device you linked to requires an external summing box, or am I wrong ?
I really hate the summing boxes. A dedicated input per loadcell is much better. And I usually only need 3 load cells. 4 would be the odd case. Never more than 4.
That is why I find the JOLLYTB interesting.
Click to expand...

Why do you dislike summing boxes? Is the corner triming the hassle?
 
On my last (actually my first and perhaps only) weigh scale project I used a summing board made by Hardy Instruments that lets me make cornering adjustments right from the HMI by isolating each load cell one by one with relays built into the summing board. The summing box is connected to a hardy plc module which sends commands to the summer serially (two extra wires in the summed load cell cable).

If you are forced to use a summing board, and want ease of use, check it out on your next project.

http://www.hardyinst.com/process_weighing/system+components/it%AE++junction+box

hardy it test.png
 
Clay B. said:
Why do you dislike summing boxes? Is the corner triming the hassle?
Click to expand...
For the following reasons:

Dumb summing boxes has no local display. A local display is invaluable in setting up and troubleshooting.

Parallel connected loadcells may generate a plausible output signal, even if one loadcell is wonly. With dedicated inputs an alarm can be automatically generated if one loadcell is bad.

If one parallelly connected loadcell is bad, to find out which one you typically have to disconnect and reconnect the parallel loadcells and see how the signals react.

The summing box itself is an extra hassle.
 

Similar Topics

B
Looking for complete Load Cell / Roller units to lay in conveyor sections
Good Afternoon, I’m limited with a skilled maintenance staff to design and build Load Cell , Rollers , etc. for conveyor sections . Do...
Replies
11
Views
660
TWS
T
B
Does Rockwell Automation have an Input that will receive an input from a Load Cell
Good Afternoon , Does Rockwell Automation have an Input Card , maybe in the 1734 series , or CompactLogix series that will receive signals...
2
Replies
15
Views
846
busarider29
busarider29
S
Looking for IS Barrier for a Load Cell Signals
Can someone recommend an Intrinsically safe barrier that can be used with an "ANALOG" load cell on a weigh scale? Load Cell is rated to be in a...
Replies
4
Views
1,375
ASF
A
C
Vibrator Speed Control using Load Cell weight
Hello All, I have two bags of two different types of peanuts hanging on a load cell above two separate feeders. I am using Studio 5000 and would...
2 3 4
Replies
45
Views
8,841
parky
P
J
Load cell monitoring
We have a web converting process that involves the web passing over rollers with load cells on each end. This provides a tension readout from an...
Replies
5
Views
2,490
kamenges
K
Back
Top Bottom