Load cell sim circuit

joeyd999

Joined Jun 6, 2011
5,237
Yet another important piece of info, thanks. The specific cell I'll be experimenting with is the LSP-2 from Transducer Techniques:

It's not a bad cell, as far as I know. How do you know the number of divisions that cell is capable of,? Is it related to its hysteresis?
I've been drinking a lot tonight, but from cursory inspection, that load cell is good for no more than 5K divisions.
 

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cmartinez

Joined Jan 17, 2007
8,220
I've been drinking a lot tonight, but from cursory inspection, that load cell is good for no more than 5K divisions.
That's exactly the same number I came up with. It means that I'm beginning to understand the fundamentals, thanks to you.

You have a nice time tonight, Joey... and a light morning tomorrow, hopefully.

We'll talk next week. Many thanks for your help.
 

strantor

Joined Oct 3, 2010
6,782
You guys are seeing something that I'm not. I thought a (any) strain gauge is truly analog and has an infinite number of divisions.
 

joeyd999

Joined Jun 6, 2011
5,237
You guys are seeing something that I'm not. I thought a (any) strain gauge is truly analog and has an infinite number of divisions.
Just from a quick Google search (I'm too drunk to write it out myself):

https://www.scalenet.com/applications/glossary.html

Divisions

The smallest increment indicated (displayed) by a scale. The amount of divisions can be determined by taking the scale's capacity divided by the scales readability (the smallest number a scale can display. Example the Ohaus SP401 features 4,000 divisions. The capacity is 400 grams and the scale's readability or another way to say it is the numbers on the display increase in 0.1 gram intervals. Therefore 400 / 0.1 = 4,000 divisions. Another example would be the Ohaus SC2020 features 20,000 divisions. The capacity for the SC2020 is 200 grams and the scale's readability is 0.01 gram. Therefore 200 / 0.01 = 20,000 divisions. It is the divisions which determines the cost of a scale - not the capacity or readability, but instead the combination of both the capacity and readability to determine the amount of divisions. The more divisions the better the quality of the weighing sensor and larger the A/D converter needed to resolve the analog output from the weigh sensor to a binary number for the digital display.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,220
You guys are seeing something that I'm not. I thought a (any) strain gauge is truly analog and has an infinite number of divisions.
The way I understand it is that the key lies in its hysteresis. I see it as inner friction that has to be given a push so that the device can break free. Since said value is of 0.02% in my load cell, that means that the number of divisions is 1/0.0002 = 5,000

Am I right?
 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,220
And of course, one can expect the load cell to fall within any number of infinitesimal places when making a measurement. But its repeatability is directly related to said hysteresis. So one could say that said load cell has a repeatability of one part in 5,000
 

joeyd999

Joined Jun 6, 2011
5,237
The way I understand it is that the key lies in its hysteresis. I see it as inner friction that has to be given a push so that the device can break free. Since said value is of 0.02% in my load cell, that means that the number of divisions is 1/0.0002 = 5,000

Am I right?
All sources of error are included in the division calculation, including drift (zero and span), non-linearity, and noise.
 

ericgibbs

Joined Jan 29, 2010
18,766
Why not simply make R2 directly proportional to Time?
hi cm,
I use a voltage so that I can simulate varying 'loads', useful if your following circuits has 'limit' sensing or ADC etc ...
Couple of samples.
E
Added: A full bridge, also asc file.
note: 1mV Offset in wt.
 

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ci139

Joined Jul 11, 2016
1,898
How do they know that full output from the cell is delivered when the sensing leg drops by 0.8% when the cell is of the 2mV/V type?
i have no idea - i studied IT not automatics nor telemechanics . . . just once had to decide whether any of the 4 load cells of the floor scale needed replacement - so i remember some pics from the service manual (muhahaa)
 
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