# 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
13
1
Hi,
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?

Satish

2. ### ericgibbs Moderator

Jan 29, 2010
8,111
1,642
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
24,331
7,600
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
13
1
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
13
1
0.819lbs/mv is it equal to 0.819lbs?
23.89C/mV equals to 23.89C?

6. ### WBahn Moderator

Mar 31, 2012
24,331
7,600
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
24,331
7,600
Does 60 miles/hour equal 60 miles?

Does \$10/hour equal \$10?

8. ### satti15790 Thread Starter New Member

Jul 17, 2017
13
1

Obviously no...

9. ### ericgibbs Moderator

Jan 29, 2010
8,111
1,642
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
13
1
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?

11. ### WBahn Moderator

Mar 31, 2012
24,331
7,600
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
13
1
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

13. ### WBahn Moderator

Mar 31, 2012
24,331
7,600
Again, 280 lb is a force. The sensor is not outputting a force. What is the ACTUAL output of the sensor?

14. ### ericgibbs Moderator

Jan 29, 2010
8,111
1,642
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.

E

15. ### satti15790 Thread Starter New Member

Jul 17, 2017
13
1

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 Moderator

Jan 29, 2010
8,111
1,642
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

17. ### satti15790 Thread Starter New Member

Jul 17, 2017
13
1
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
24,331
7,600
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
13
1
---> 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
368
128
With the four numbers sets, I get a smooth X/Y curve as follows:

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