2
\$\begingroup\$

I have the WK-06-12BT-350 ohm WK125BT Strain gauge from Vishay the Gauge comes equipped with 4 wires ( High endurance lead wires). The following document describes a similar gauge: Strain Gauge is it possible to convert the following gauge to a 2 wire connection? are the additional wires negligible? or they might cause measurement errors if left open?

The acquisition machine can accept 2 or 3 wiring scheme but not 4 furthermore the strain gauge will be part of a quarter bridge connection for a fatigue test running at am excitation voltage of 5V

Thank you Much appreciated

\$\endgroup\$
  • \$\begingroup\$ Provide a link to the exact part you want to use. \$\endgroup\$ – Andy aka May 19 '17 at 16:10
  • \$\begingroup\$ What are you connecting this to? I have a strong feeling what you're trying to do isn't going to work no matter how you connect it. \$\endgroup\$ – Matt Young May 19 '17 at 17:29
  • \$\begingroup\$ I have a data acquisition C series module unit from NI (National instruments) for the CompactDAQ System \$\endgroup\$ – chaosmind May 19 '17 at 18:56
2
\$\begingroup\$

The WK125BT Strain Gauge you have is only a single gauge, not a bridge (half or full).
enter image description here
So if it has 4 wires, then these would allow you to use the 4-wire, single-gauge method described in your second link if you want to.
enter image description here
Using the 4-wire method lets you achieve greater accuracy by allowing you to (mostly) ignore the resistance of the wiring.
In this case you would use a constant-current source to energize the gauge through the outer wire pair, and take your measurement across the inner pair.

\$\endgroup\$
  • \$\begingroup\$ Yes, but my data acquisition unit is an NI re configurable module it provides internal resistance to complete a Wheatstone bridge connection can be made as quarter, half or full. I would like to only use two wires of the gauge I have and ignore the others, I can trim them to avoid wire resistance and open circuit across those, I would like to know if that is a solution or if I can connect them 3 wire without major effects while ignoring the 4th \$\endgroup\$ – chaosmind May 19 '17 at 18:55
1
\$\begingroup\$

The most basic connection using only 2 wires gives you a current path through the strain gage with no compensation for added wire resistance. Four wires gives you 2 wires for each connection, one set for the excitation current and one set to measure the voltage drop across the strain gage. Three wires gives you one extra conductor of the same length and gage as the other two, which is used by your instrumentation to "measure" the lead resistance of one lead, then predict and compensate for the lead resistance in the other two leads during the data acquisition. If all 4 conductors are the same length and wire gauge then you can use a 4-conductor cable in a 3-wire connection by leaving one conductor unconnected/open.

If your instrumentation has the ability to 'zero' the reading to offset the wire resistance then 2 wires should work ok. In that case you could use 1 wire to each side of the strain gauge, and leave unused wires disconnected. The electronic instrument would basically be providing a differential reading (the amount of change from your zeroed condition).

\$\endgroup\$
  • \$\begingroup\$ 3 Wire connection will need a major modification in connection cables, is it possible to ignore 2 leads and connect two ?if that might provide a high error in accuracy I will have to modify the connections, Thank you \$\endgroup\$ – chaosmind May 19 '17 at 16:59
  • \$\begingroup\$ If your instrumentation has the ability to 'zero' the reading to offset the wire resistance then 2 wires should work ok. In that case you could use 1 wire to each side of the strain gauge, and leave unused wires disconnected. The electronic instrument would basically be providing a differential reading (the amount of change from your zeroed condition). \$\endgroup\$ – Entrepreneur May 20 '17 at 13:16
  • \$\begingroup\$ Great Thank you! I will test the gauge with an ohm meter as previously mentioned in an answer to check the effect and I can zero the gauge in software/instrument.. much appreciated \$\endgroup\$ – chaosmind May 22 '17 at 17:51
0
\$\begingroup\$

A strain gauge bridge is usually a Wheatstone bridge with 4 elements, or it could be a simple half bridge with only two elements. In both cases there is no such setup with two wires.

enter image description here enter image description here

You could also make a Wheatstone bridge with three fixed resistors and one single gauge, but it is recommended to put everything close to the gauge, so again you have 4 wires.

enter image description here

Note that power supply has two wires and the voltmeter in the pictures is DAQ input 2 wires

\$\endgroup\$
  • 1
    \$\begingroup\$ Thank you for the reply, the Strain gauge has 4 leads for connection, I would like to only use two of those to avoid major modifications in the per-soldered connection wires \$\endgroup\$ – chaosmind May 19 '17 at 16:57
  • \$\begingroup\$ @chaosmind Then join them together in pairs. Measure with ohm meter which wires are internally connected together. \$\endgroup\$ – Marko Buršič May 19 '17 at 18:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.