I am writing to request a recommendation for our situation (which I believe is a fairly generic one): We are making measurements using a strain gage, with the parameters as follows:
Excitation voltage = 5 V; Sensitivity = 5 mV / V; Desired sample rate for measurement = 1 kHz or greater; Desired ADC resolution = 18 bits or greater
Can you propose a design that would allow us to make such a measurement with our strain gages? We would appreciate either a generic schematic (or app-note), or else a recommendation in terms of specific parts. I presume this would involve an ADC such as the ADS1252, in addition to an opamp and a high-precision voltage reference.
The reason we are searching for a TI-verified design is because we would like to expedite our prototype-and-production time for this particular measurement; We have looked through the application notes of some ADCs and haven't yet found a close enough match to our particular situation, hence I am bringing this question up here.
Here is a web page with bridge sensor information and design considerations.
The specific information revolves around the ADS123x family of parts, but they do not meet the 1ksps requirement. The ADS1252 is a good part, but you will need some external gain as there is not a PGA associated with this part. You might consider the ADS1255, which has a PGA with a gain up to 64.
The ADS1259 is a very low noise delta-sigma that also requires some gain stage at the front end. You could consider using the OPA333 as the amplifier between the strain gauge and the ADC. There are numerous other op amps that could be considered as well.
Appreciate the pointers. I have one other question...
First, thank you for the three part recommendations. I intend to use the ADS1252 along with an OPA333 for pre-amplification.
Secondly, we do have an alternate application for which the slower-sampling but PGA-integrated ADS123x family seems to be appropriate (especially given that much app-note information is available for this part).
Can you provide (or refer me to a link for) existent example microcontroller pseudocode/source-code/firmware for interfacing with the ADS123x family, or for any ADC with an equivalently simple data interface ?
TI has a new family of products called SensorAFE's. It provides a easy to use development platform along with the MCU code library,You can take a look at LMP90100 family of products here:http://www.ti.com/product/lmp90100#parametric , It has max data rate of 214 Sps.
There is a code library for interfacing LMP90100 devices with any MSP430 family devices,which can be found here :1. App Note,http://www.ti.com/lit/an/snaa134/snaa134.pdf2. Code, http://www.ti.com/litv/zip/snac029
We have a load cell reference design using the ADS1232 called the ADS1232REF. This board is controlled by a MSP430F449, which has a built in LCD controller. All files and code pertaining to this board can be found and downloaded from:
All digital control (Speed, Mux, etc.) in this design is GPIO from the micro. This is not necessary unless this specific control is needed. The pins can be tied high or low appropriately. The SPI interface uses the built in hardware peripheral of the micro. The code example is built with GCC along with freeRTOS code. This can sometimes be difficult to follow, but the primary initialization and communication to the ADS1232 is in the 'c' file 'ads1232.c.'
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