The goal of my project that I need help with is to measure pressure in mmHg between two surfaces.
I am using this basic force sensor setup that I found on the Arduino Get Started website.
For more context on the application, imagine you are putting this force sensor on a book that is a few millimeters thick and clipping a clothespin on it to read the amount of pressure that the clothespin is exerted when clipped onto the book. What is the best way to go about this? Is my current setup a good start? How can I convert the output of this code that I am using to tell me mmHg?
The tutorial mentions that this sensor is not much good for measuring weight and the example code just reports a squeeze of none, light, medium and big.
Is your explanation with the clothespin actually what you are really going to do? Calibrating your proposed sensor in mmHg will be problematic.
If a "puck" is adhered to both sides of the sensor, and other guidance in the Tekscan mechanical and electrical application guides is followed, then the sensor could be calibrated with known forces and the resulting pressures[*] on the puck/sensor could be calculated.
Do you know that what you are asking relates to a barometer and indicates the atmospheric pressure as the height of a mercury column in a vacuum? It also works for a water column, except water evaporates quicker than mercury.
Hi Paul, thank you for your comments. The code does not tell me mmHg; it reads the type of "squeeze". The pressure is not atmospheric pressure- more of a force.
Hi Emily, thank you for your response. I missed that it was not good for measuring weight. For all intents and purposes, imagine that yes the clothespin idea is what we're trying to do.
I'm not suggesting you purchase Tekscan software or sensors.
I'm saying you should carefully read both Tekscan "Integration Guides." If you follow their recommendations, then you should be able to achieve your goal, with the sensor you already have at hand. (Keeping in mind that it is not a precision instrument.)
Edit to add:
Although your sensor's resistance-to-force relationship is highly nonlinear, if you use the Tekscan recommended op amp circuit, you will get a reasonably linear force-to-voltage relationship.
Provided that your accuracy and precision requirements are not very demanding (as it seems), and provided that you follow the Integration Guide recommendations, then an FSR may be just fine for your project.
Also, as I mentioned in Post #4, your choice of units is odd.
If you are interested in "more of a force" then why did you pick mmHg, which is "pressure" and normally used for things like blood pressure and air pressure, not clothespin "pressure."
The resistance of a "Force Sensitive Resistor" is not simply related to either force or pressure, and such a sensor is difficult to impossible to calibrate for meaningful measurements.
If you actually want to measure a quantity, choose the right sensor. In your case a strain gauge force sensor might be useful.
The "force" of the air on the free end of the curved tube is what the barometer is measuring by moving the mercury column up or down so many millimeters. Nothing more, nothing less. mmHg has no bearing on what you are proposing.
If you can measure the FORCE (and @jremington is right a load cell is a better instrument for doing that)
then pressure = force / area
so given the size of your plates and knowing the force (in newtons, or kgf or whatever) you can calculate the pressure in bar, mmHg, or any units you wish.