Sensor/switch for package weight verification


Thread Starter


I am looking for a sensor or a switch to verify that I have product in a box. The empty box weighs a little under 1 ounce and the box with product in it weighs over 4 ounces. I would think that a simple device that could do this job might exist, just don't know what. Thanks for your help.


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I did something similar a while back, but the weight was quite a bit more. The check point was a roller platform mounted on linear guide posts, similar to what die makers would use on a die set, but the weight was supported by a center mounted air spring. Try these two addresses for more info.
The force was adjusted by air pressure and as soon as the weight overcame the air pressure, the platform dropped about half an inch and tripped a switch. You'll have to find something that will work with your very light weight requirement. It is possible that your switch resistance might be more than the 4 ounce. The best choice would be a load cell, but the cost is a little higher because of the required instrumentation. Try
A different approach might to be to use a capacitive proximity switch, adjusted to "see" through the cardboard, and detect whether an object is inside the box or not. This would only indicate the existance of something, but not the quantity or weight of what is inside.

Adolfo Jimmy Saldivias


If you want to do it with the box closed, you will need a weighting device.
How fast are the boxes passing by?
If you can check it with the box opened, you can use any photoelectric proximity switch. You can check examples of this on
Or at
Or at
Or at
Or at any manufacturer of photoelectric sensors.
I hope it helps.

MBA Ing. Jimmy Saldivias
Phone: 591-4-523438
Fax: 591-4-523413
The box will be closed so a prox won't do the trick. The cyle time will be 30 a minute. I looked into the load cells and they seem like a good solution. I think that is what I will end up using. If anyone has any other ideas I would like to hear them. Thanks for the quick response and great ideas!


James Bouchard

There are a number of companies that make check weighers for this application. Loma and High Speed Check Weighers are two companies that come
to mind. If you are considering the use of load cells you are probably better to purchase an off the shelf system than spend all that time
reinventing the wheel.

James Bouchard
brad, if you havent solved this load switch yet, my co. makes force activated switches, setable to within .1%f.s 1lb to 100,000 lb please call if your interested.

alan paine
force switch corp.