Disassemble a load cell? - Page 1
Forum section: electronics / projects

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2022, 10:04:44 am
content: I would like to experiment with some strain gauges, but don't really want to wait months for an order to come from China.I have a load cell at hand, and was wondering if anyone was successful by removing the white goo from the load cell and extracting the strain gauge?A load cell like this:https://electropeak.com/pub/media/catalog/product/cache/fa232c603e0403143aafcf902b42df2f/_/s/_s_e_sen-13-045-1.jpg

author: jonpaul
author_rank: Super Contributor
timestamp: March 12, 2022, 10:43:51 am
content: DIY make thin PCB, see typical strain guage pattern, bond to any desired metal beam, sheet, extrusions.Use 4 wire resistance measures or 6.5 digits DVMBon courageJon

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2022, 11:05:23 am
content: I want to measure on a length of 550mm, maybe even the 1.6mm standard size would be okay? What kind of performance can I expect from soemthing like this?I haven't found any larger strain gauge for those dimensions.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2022, 11:18:34 am
content: 1.6 mm wire is rather thick and would mean very small resistance.Just for demonstration one could try some thin (e.g. 0.2) constantan or manganin wire. The restance would still be relatively small (e.g. 10 Ohms range).The train effect for metalls is relatively similar: a resistance change of about 2 times the strain. So 0.5% of strain (which is about the maximum for a strong material) would result in 1% of resistance change. To avoid creepage and with softer maerials one may have to use less strain.One usually uses a bridge with 2 or 4 equal resistors to compensate the temperature effect.edit: The glue to attach the strain gages need to very strong and it would be very hard to remove them, with a large chance to damage the strain gage.

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2022, 11:23:11 am
content: Sorry, I meant 1.6mm thick PCB with a strain gauge pattern on it.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2022, 12:58:18 pm
content: Using PCB material has 4 problems:1) The FR 4 material can show creepage / elastic relaxation2) pure copper can not withstand much stress and will also plastically deform, so the maximum strain is limited (e.g. 0.01% or 8 m bending radius)3) copper resistance is quite temperature dependentthis could be partially compensated by building a bridge circuit, with resistors on both sides of the PCB.4) the copper resistance is quite low - so it would need a relatively fine wire pattern to get a reasonable voltage.

author: jonpaul
author_rank: Super Contributor
timestamp: March 12, 2022, 01:14:33 pm
content: Hello again: in 60 sec found$12 Amazon....Culler Strain Gauge Used in Mechanics Experiment for Material,https://www.amazon.com/Culler-Mechanics-Experiment-Material-Industry/dp/B01FUNXN0KThey are stick on ready made strain guages, on Mylar or Kynar?similar are used in aviation and materials stress tests.Not precision but fine for familizaration...Jon

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2022, 01:33:29 pm
content: Yeah, I found other ones too, I just wanted to see what can I make now without waiting for the shipping.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2022, 01:37:30 pm
content: With a PCB one may have to wait for the PCB to be made. With thin lines and double sided PCB etching at home is not that much fun.

author: mrburnzie
author_rank: Regular Contributor
timestamp: March 12, 2022, 02:07:50 pm
content: I guess ordering is the option here.