Conversion Process from mv to lbs

Discussion in 'Embedded Systems and Microcontrollers' started by satti15790, Jul 17, 2017.

  1. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    Hi,
    Can you please help me in conversion formulas
    Is there any direct formula to
    Convert millivolts to lbs?
    Convert Hz to rpm?
    Convert millivolts to °C?

    if not, these are my requirements
    Input:0-1880mv±5mv
    Output:0-1540lbs ±10lbs

    One more,

    Input:0mv-29.3mv±75µv
    Output:0-700°C ±4°C

    if Possible can you provide explanation?

    Thanks in advance

    Satish
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    To get a Scaling Factor, divide 1540lbs/1880mV = 0.819lbs/mV

    700C/29.3mV = 23.89C/mV

    Is this what you are asking, what is the application.?
    Normally you would configure an amplifier to do the scaling,

    E
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    Where are these needs coming from?

    It's like asking if there is a direct conversion from liters to kilometer/hour.

    Exactly what is it that your inputs and outputs represent?

    Based on what little you've given, here are your "formulas":

    mv to lbs: 819 lb/V
    mV to °C: 23.9 °C/mV

    You haven't aid what your input/output spec is for the Hz to rpm, so that's up in the air.
     
  4. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    Yes is there any direct conversion?

    Those inputs are coming from sensors...
    so if i read 1880mv as input i should convert that value to lbs i.e 1540lbs
     
  5. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    0.819lbs/mv is it equal to 0.819lbs?
    23.89C/mV equals to 23.89C?
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    That's not a direct conversion. It's a scaling process. You millivolts don't somehow become a force or become heat.

    You have a sensor that produces so many millivolts per pound that is applied to it. You then want to scale that voltage so that it has a nice, convenient relationship.

    Your output is not pounds (unless you have some actuator that is taking that signal and producing a load on something). You have a voltage that you want to interpret as indicating what load is acting on the sensor.

    If you have 1000 lb as your input load, what voltage do you need in order for your meter or gauge or whatever you are using to indicate 1000 lb?
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    Does 60 miles/hour equal 60 miles?

    Does $10/hour equal $10?
     
  8. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    Obviously no...
     
  9. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi S,
    Most electrical sensors give an output which is proportional to the parameter which the sensor is being used to measure.

    For example:
    a simple fuel tank sensor will give a electrical signal which is proportional to the amount of fuel in the tank.
    As a human, if I was presented with a gauge that gave me the fuel level in millivolts I would have to mentally convert it into gallons or litres.
    That would be a pain in the rear, as every vehicle I drove would probably have a different sensor, so by Scaling the sensor value, we normalise the display reading.

    The display gauge is scaled so that I see a reading of gallons or litres.

    E
     
  10. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    ok I got it... But in my case some example values are like this

    Input : 785mv ----------------> output:280lbs
    Input : 1131mv ----------------> output:670lbs
    Input : 1880mv ----------------> output:1540lbs

    As above you mentioned ur scaling will work only for last value... Can you make it generic? if Possible
    I think u got my point?

    Thanks in Advance
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    What kind of thing are you using that has a voltage for an input and produces a force as an output? Is it some kind of hydraulic actuator?

    Whatever it is, your response is very nonlinear, so you need to characterize it to determine how best to model it.

    What, exactly, is it you are doing?
     
  12. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    We have some sensors which are related to Jet Fighter Aircraft...
    Those sensors will give inputs to the Engine, from Engine we should read those and convert and Display,this is the actual procedure

    Sample inputs from Sensors are Temperature,RPM,Fuel etc

    If Fuel Sensor input is 785mV, then the output should be 280lbs...
    Similarly as mentioned previous....
    I hope u understood

    Thanks in advance...
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    Again, 280 lb is a force. The sensor is not outputting a force. What is the ACTUAL output of the sensor?
     
  14. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi satti,
    Are you saying that the fuel sensor is giving an output of 785mV for 280lbs 'weight' of fuel in a tank.????

    IF the sensor output versus lbs weight was linear, you could say the sensor would output 2.66mV/lb.
    but if the sensor versus lbs is not linear, you will have to determine the relationship, either by measurement or referring to the sensor manufacturers data.

    We need much more information from you, in order to give meaningful advice.

    E
     
  15. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    Hi Gibbs thank you for your reply...

    Ok let me explain in detail...

    Sample flow of project

    Sensors----->Controller(MSP430)-------->Display
    So Controller will read some data from sensors and process the data and Send to Display
    For Example Sensors will give some output 785mV to Controller, Controller need to process and give the output as 280lbs to Display

    Here are some of sample sensor outputs
    785mv ---------------->280lbs
    1131mv ----------------> 670lbs
    1880mv ----------------> 1540lbs
    sensor output range (0 to 1880mV)--------------------->Data processing(0 to 1540lbs)

    Customer not provided any sensor data sheet... These values are not linear
    So if there is any possibility to make generic conversion for above values

    Hope u understood...
    Thanks
     
  16. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi s,
    I follow what you are asking, the problem is that there are only 3 data points, not really enough to form an reliable equation.
    Is it possible to post more data points.?

    Is this project for a safety critical application or just a college assignment.??

    E

    A02.gif
     
  17. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    No, I dont have other data points... Customer provided only these data points
    This project is not a college assignment... I am working for Aeronautical related company...
    This project belongs to Fighter Aircraft...
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    With only three points you only have a few reasonable things. You can use a piecewise linear fit, you can use a quadratic fit, or you could try to do some kind of spline fit, though I don't know if three points is enough.

    It sounds like you are trying to take a VOLTAGE signal out from your sensor and then drive some kind of display that will indicated in the proper units. What kind of display are you using?

    But at one point you mentioned taking the signal from the engine, which got its signal from the sensor. Is the engine just buffering the signal and making it available to you?

    Does anyone at this aeronautical related company have any electronics background?
     
  19. satti15790

    Thread Starter New Member

    Jul 17, 2017
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    ---> Yup

    It's like an back light LED Display...
    I dont have any other data points....
    Yes, the engine is just buffering the signal...
     
  20. Kjeldgaard

    Member

    Apr 7, 2016
    188
    62
    With the four numbers sets, I get a smooth X/Y curve as follows:
    Fuel_1.jpg

    And it looks wrong with sets 2 and/or 3?
     
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