[SOLVED] Need to read the resistance value from a sensor

[Dont]

Hi,
I'm having a sensor which gives a various resistance as a output when the input gets varied.

The resistance ranges is from 10 to 180E for various input. So what I'm planning is connecting a known resistor value in series with the unknown resistance and make it as a voltage divider by applying 12V as a main VCC and get the voltage and then process it.

My doubt is what should be the resistance wattage should be used for this? and how to avoid any sudden spikes from the divided voltage if at all occurs. My expected range is 0 to 5V for which I want to process.

Hope my question is clear

 

[crutschow]

What resistance is 180E?
Is that 180Ω?
Is that resistance to ground?

 

[ud23]

Hi,
I'm having a sensor which gives a various resistance as a output when the input gets varied.

The resistance ranges is from 10 to 180E for various input. So what I'm planning is connecting a known resistor value in series with the unknown resistance and make it as a voltage divider by applying 12V as a main VCC and get the voltage and then process it.

My doubt is what should be the resistance wattage should be used for this? and how to avoid any sudden spikes from the divided voltage if at all occurs. My expected range is 0 to 5V for which I want to process.

Hope my question is clear

I assume you are having the sensor like some what RTD pt-100 temperature sensor.If so then will need at least 1% or 0.5%(if you get at your place) tolerance resistor at your voltage divider and for spike and other noise you need to use RC filter.But make sure your Divider supply 12V VCC should be stable and noise free.

 

[Dont]

What resistance is 180E?
Is that 180Ω?
Is that resistance to ground?

Yes it is to ground...

 

[Dont]

I assume you are having the sensor like some what RTD pt-100 temperature sensor.If so then will need at least 1% or 0.5%(if you get at your place) tolerance resistor at your voltage divider and for spike and other noise you need to use RC filter.But make sure your Divider supply 12V VCC should be stable and noise free.

I dont have problem with the tolerance of resistor. What I want to know is how many watt resistor should I use? and regarding my 12V will be from battery.

 

[ud23]

5watt or less then 5watt if you are using temperature sensor with measurement for higher temperature.

http://www.electronics-tutorials.ws/resistor/res_7.html
http://www.robogaia.com/how-to-calculate-resistor-wattage.html

 

[FvM]

In a first order you should worry about the acceptable voltage/current/wattage of the sensor. It's no problem to chose a reference resistor with any required power rating, but exceeding the sensor's suggested operation conditions can cause measurement error or even sensor damage. What's the specification?

 

[asdf44]

Your resistor idea is valid but it's also easy to construct a current source (TL431, opamp, LM317) which would give you a linear relationship between sensor voltage and R. This may or may not be an advantage.