Hello EveryBody!
I am designing a measuring system for strain gauges data measurement. For that i need a mux(16 x 1). But i am confused on which basis should i select it.
Can any one help me?
Looking forward for your suggestions!
Regards
Awais
For the 16x1 mux, you have 4 input selection. The output consider the input line according to the following table:
0 0 0 0 Input number one
0 0 0 1 Number two
0 0 1 0 Number three
And so on until the last input is taken when the selection is 1 1 1 1
As you selected 16:1 mux,
means you knows that 24=16
hence it is 4 input and a output.
now with 4 inputs you have 16 different signals can utilized.
When strain gauges are used, they are usually connected in Wheatstone bridge circuit since strain gauge resistance changes very little, and what you actually measure is voltage. Voltage is measured in output terminals of the bridge, so measuring system should be with 16-channel high-impedance differential voltage inputs.
Under assumption that each strain gauge has its own bridge, you will need 16-channel differential analog multiplexer, (16:1)x2, at input. It may be found in one IC or can be created by combining more IC with different configurations, ex. 2 IC (16:1)x1 or 4 IC (8x1)x1. Since almost nor current is passing through switch, On-resistance is not critical. Also resistance of the strain gauges is low (most common 120om and 350om), and equivalent resistance of bridge output will be low, isolation resistance of nowadays analog multiplexers will not be critical to. So most of analog multiplexers will do the job.
From standard CMOS family you can use ex. 2 integrated circuit 4067, (16:1)x1 channel each, or 4 IC 4051, (8:1)x1. There are many choices from Analog Devices, ex. one of solutions with single IC in (16:1)x2 configuration is ADG726.
http://www.analog.com/en/switchesmultiplexers/multiplexers-muxes/products/index.html
http://www.nxp.com/documents/data_sheet/HEF4067B.pdf
Hi,
As you are talking about MUX selection for strain gauge data measuring system, you should ponder upon Analog MUX. There is absolutely no question of digital logic. I second the last answer by Mr. Lavdim. You need 16 channel analog MUX. For basic point of these analog MUXes, you can follow this link.
http://www.keysight.com/upload/cmc_upload/All/1355A_manual.pdf?&cc=IN&lc=eng
Then try to search for different available analog MUX by various vendors like (TI and Analog Devices, etc.)
Selection of the mux will depend strongly on the circuitry you use in your application - e.g. if output of the mux is connected directly to a non-inverting input of an op-amp, the mux does not have to be low-ohmic, as its internal resistance will be negligible in comparison to the op-amp input impedance. This is quite important, because low-ohmic muxes have usually much higher leakage current which will introduce additional offset when flowing through the bridge. In the case of a strain gauge the mux bandwidth and speed of switching are usually non-critical (any will do), but check them for PSRR (the higher, the better) as you will probably work with low level signals.
Hi,
so, it is possible to use only two MUX !!!
In this case,the technique of data measurement was to measure the differential voltage at the Wheatstone bridge terminals which are fed to entry of the 2 multiplexers!!!! Thanks
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