Hello,
I need a way to weight 25g, 100g and 200g with an accuracy of +/- 1g. I searched for load cells and came first across the Modell of SeeedStudio which is specified as ranging from 0 - 500g robotshop.com/eu/en/micro-load-cell.html, but in the according WikiPage of the producer, the cell only starts to show a voltage greater 0 when a weight over 150g is placed on the load cell. This seems not appropriate for my project.
Does anyone have some experience with this or another model of load cells? Is it possible to weight from 0g with this one: robotshop.com/eu/en/micro-lo … 78-kg.html? And if yes, can the Phidgets Load Cells be used without the Phidgets board?
Thanks in Advance!
Tanja
Hi Tanja,
Here are answers to your questions/comments:
To get accurate measurements with load cells, you need a few things:
]The full scale of the load cell must be as close as possible to the expected force you will be measuring. For example, if you wish to measure weights of 80-100 g, you would use a 100 g load cell./:m]
]The proper amplification of the signal of the load cell must be done. Load cells typically output voltage variances of 1 mV / V of excitation. Therefore, a typical load cell with an excitation voltage of 3.3 V DC would only vary its output by ~ 3.3 mV DC for the full scale./:m]
]The system used to measure the amplified output (usually and ADC) needs to be setup for the right range of voltage, so as to be as precise / with the largest range as possible./:m]
This is rather an unusual issue. We recommend that you check out the Phidgets load cells then, as they did not exhibit this behavior when we tested them (they report a value for the full scale, or FS).
You can check out our blog posts about a Wheatstone bridge amplifier here and here. We use Phidgets load cells in those articles.
Concerning the Phidgets board, you do not have to use that one specifically, but you will need a amplifier of some kind, as microcontrollers and other ADC circuits usually cannot read such a small signal range (0-3 mV DC). For example, an Arduino microcontroller board using its ADC over a 3.3 V DC range at 10 bits resolution has a maximum theoretical resolution of ~3.22 mV, which means that the entire range of the load cell would appear to the Arduino ADC as noise, if connected to it directly.
Sincerely,
