My question is how to read ratiometric sensor output like 5V: %10Vs to %95 Vs?
Do I need to use amplifier? If I had an option should I choose regulated 0-5V output sensor and what is advantage of that?
\$\begingroup\$
\$\endgroup\$
Add a comment
|
1 Answer
\$\begingroup\$
\$\endgroup\$
4
A ratiometric sensor's output is irrelevant if you don't consider the power supply voltage that feeds it therefore, such devices as RTDs can use a pull-up resistor to form a potential divider and an ADC uses the supply to the pull-up resistor as its reference - that is a ratiometeric method of obtaining the value of the RTD.
If you are just wanting to transmit an analogue value down some simple cable to something that reads it then you can't really use a ratiometric method because you don't have a measurement of the excitation voltage on the device. This is why on remote strain gauge bridges sense wires are used to ensure that cable volt drop is factored into the measurment i.e. the terminal excitation voltage across the device is remotely held constant.
If you have a sensor that provides a fixed voltage (or current) output irrespective of the supply voltage (such as an AD590) then you are forced away from the simple ratiometric measurment method and (if using an ADC) you have to have a fairly precise reference voltage by which you make comparisons.
If i had an option should i choose regulated 0-5v output sensor and what is advantage of that?
Go simple first and try ratiometric. If this can't deliver the accuracy then a different sensor might be needed or a different method of communications between sensor and receiver.
Do i need to use amplifier?
Not always
-
\$\begingroup\$ Thanks fir detsil response Andy. Can we say electrically no difference both can be readed using analog input interface. Anyway if amplifier is not always used that depends on what? \$\endgroup\$– Soso5Commented Oct 30, 2015 at 9:04
-
\$\begingroup\$ If the sensor signal is small (such as from a strain gauge) then amplification is usually a very good idea. If the ADC reference is stable both ratiometric and non-ratiometric measurments are feasible. If reference is a little undefined then only ratimetric measurements can be accurate. \$\endgroup\$– Andy akaCommented Oct 30, 2015 at 9:07
-
\$\begingroup\$ For better understanding amplification necessity when you say "small" you mean voltage or current? How can i say it is small or not. Thanks. \$\endgroup\$– Soso5Commented Oct 30, 2015 at 9:13
-
\$\begingroup\$ It depends on the output voltage range of the sensor compared to the imput voltage range of the ADC - less than 50% might cause you to consider using an amplifier - less than 10% and you would strongly consider using an amplifer to make maximum usage of the ADCs resolution. \$\endgroup\$– Andy akaCommented Oct 30, 2015 at 9:18