I measured black-red = 400ohm, green-white = 350ohm in a 5kg loadcell.
How can I calculate the resistor values?
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\$\begingroup\$ Does the bridge have a datasheet? Does it have a fifth resistor (in series with one of the input wires)? \$\endgroup\$– devnullCommented Apr 19, 2022 at 11:27
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\$\begingroup\$ Measurements are meaningless because of connections. \$\endgroup\$– StainlessSteelRatCommented Apr 19, 2022 at 13:45
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2 Answers
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Many strain gauges have gain calibration resistors in the excitation leads such as here: -
Image from RS, Tedea Huntleigh Wire Lead Load Cell. And, this means that the excitation leads measure a higher resistance than the output leads. Given also that 350 Ω is pretty commonplace for a strain gauge, it's likely that the measurement of 400 Ω is because of the 350 Ω gauges plus 25 Ω in each excitation lead.
- Resistance between A and C should be 287.5 Ω nominal
- Resistance between A and D should be 287.5 Ω nominal
- Resistance between F and C should be 287.5 Ω nominal
- Resistance between F and D should be 287.5 Ω nominal
$$R_{AC} = 25 + 350 || 1050$$
answered Apr 19, 2022 at 11:54
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\$\begingroup\$ ok, i get it now, how did you calculate and got 287.5? I just got 290ohm AC, AD, FC, FD \$\endgroup\$ Commented Apr 19, 2022 at 13:26
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\$\begingroup\$ guang ce yzc 1b 5kg loadcell \$\endgroup\$ Commented Apr 19, 2022 at 13:26
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2\$\begingroup\$ @TumenbayarMunkhjargal between B and C is a 350 ohm gauge in parallel with 3 series gauges of 350 ohm. That is a resistance of 262.5 ohms. Therefore between A and C is 262.5 ohm plus 25 ohm = 287.5 ohm. \$\endgroup\$– Andy akaCommented Apr 19, 2022 at 13:28
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\$\begingroup\$ could you please simplify that delta circuit into simple so I can understand it fully \$\endgroup\$ Commented Apr 19, 2022 at 13:34
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1\$\begingroup\$ I've added a picture @TumenbayarMunkhjargal \$\endgroup\$– Andy akaCommented Apr 19, 2022 at 13:41
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This is a possible solution:
You could check by performing other measurements:
between A and C = 312.5 \$\Omega\$
between A and D = 312.5 \$\Omega\$
between E and D = 262.5 \$\Omega\$
between E and C = 262.5 \$\Omega\$
Just to be clear: if this is the topology you don't have access to node B.
guang ce yzc 1b 5kg loadcell
Update: different to this document, which resembles a datasheet and was mentioned yesterday in another question, it seems that the internal configuration uses 2 series resistors, as detailed in Andy's answer.
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\$\begingroup\$ it is physically loadcell 5kg, how to calculate it, not practically \$\endgroup\$ Commented Apr 19, 2022 at 12:20
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\$\begingroup\$ A and C, AD, ED, EC are all 290ohm as I measured just now, I wonder why \$\endgroup\$ Commented Apr 19, 2022 at 12:58
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2\$\begingroup\$ @TumenbayarMunkhjargal looks like the answer you have been given is correct, with the tolerance of what you say you measured compared to the 287.5 ohms suggested. \$\endgroup\$ Commented Apr 19, 2022 at 13:25