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Hello Forum,
I am working on a design that uses a piezoelectric load cell. I need to condition the load cell O/P so that we can accurately measure the load applied using the uP ADC.
The AFE has a few complicating factors:
1) the load cells have offset (no load applied) characteristics: min -20mV to max +2mV.
2) The load cells have sensitivity characteristics: Min 1.6 mV/Vsupply/Nload to max 3 mV/Vsupply/Nload. (Load cell O/P is a differential voltage biased at Vsupply/2 and is always positive when load is applied except for initial offset)
Design is very cost sensitive so I want to use as few components as possible to implement the AFE conditioning circuit. I am considering using a single TLV333 opamp that has very low offset and drift characteristics in differential mode. I can add offsets easily enough to counter the load cell offsets. However my biggest problem right now is the sensitivity variation between cells (almost a factor of 2). This halves the range available when the sensitivity of a particular cell is at the minimum specified (we have to design for the highest sensitivity so that we don't saturate the amplifier). That reduces the resolution with min sensitivity load cells available in the ADC.
I've searched around but I can't find a suitable (low cost) diff amp with relatively simple programmable gain feature. Right now the gain I need is approximately in the range 45 to 90. Ideally it should be an I2C controlled device (SPI at a stretch). Even a 2 or three step gain change device would probably suffice. Ideally the device would have adjustable offset trim as well.
We will calibrate each device in production so offset cancellation and gain setting is possible.
The design is single rail with supply at 3.3V dc. I would really appreciate it if someone could have a look at this for me.
Thanks in advance,
JB.
Hi John,
This looks like a double post. I will close this one and keep the other one open.