That circuit is a quarter bridge with an INA125 instrumentation amp which has 16 inputs while I am using a half bridge with a 741 op amp which has 8 inputs. While its not the same circuit it has given me some ideas to debug my circuit.
You are correct about the instrumentation amplifier, I should have used a better amp than the 741 but I am out of time thus I must use what I have and make it work. A bridge is classified by how many active elements are in the bridge, mine has two thus is a half bridge. The most frustrating part is that we utilized the same configuration, only with a quarter bridge, and a 741 op amp to measure pressure in a pressure vessel in a lab and it worked fine. The difference being that we measured the output using a very sensitive multimeter and I no longer have that luxury.
Well I would very much dispute your definition of various bridge configurations.
While the circuit is indisputably a Wheatstone bridge, when naming strain gauge configurations one considers the number of active arms. The OP's configuration is called a half bridge circuit by those familiar with the terminology and can be verified by reading the data sheet for a common strain gauge amplifier from Analog Devices 5B38.pdf
Quote from: PapaG on Nov 30, 2012, 05:43 pmWhile the circuit is indisputably a Wheatstone bridge, when naming strain gauge configurations one considers the number of active arms. The OP's configuration is called a half bridge circuit by those familiar with the terminology and can be verified by reading the data sheet for a common strain gauge amplifier from Analog Devices 5B38.pdfYour link is broken, maybe it's only a half or quarter link?
Well that doesn't change my definition of what a full bridge configurations is or is not. The Figure 3 5B38 Input Field Connections picture in that doc clearly shows the different configurations and how many elements are used. A full bridge uses four elements regardless of which of the four are variable or not. The other two are simply set up as a simple two element voltage divider. I would never call a simple two element resistive voltage divider a 'bridge circuit', half, quarter, or otherwise. The OP showed us a crude drawing of a four element bridge with two fixed resistors and two variable load cell resistors (disregarding his attempt at adding a null adjustment pot), wired in a full bridge configuration, end of story. Lefty
First off all insolence to is completely unnecessary especially to someone seeking advice.
I think possibly what AD and you and the OP are trying to state is that load cells come in several styles where the load cell itself makes up either all four elements of a full bridge (four output wires) or just two (three output wires provided) or one of the elements (two output wires provided) needed to be wired up to the rest of the input circuit to complete a full bridge configuration. Hows that for a compromise ?
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