Lab 1 Part 3 Pressure Transducers - MAE221/Thermodynamics-Lab GitHub Wiki

A Sensor for the Measurement Pressure

Objectives

Explore the uses of a pressure sensor
Understand a U Tube Manometer
Explore the Maximum Inspiratory Pressure (MIP) and Maximum Expiratory Pressure (MEP) you can achieve with your lungs
Record max MIP and MEP using your Photon
Finish the worksheet

Introduction

The last sensor we are going to explore is a pressure transducer. The P-V-T diagram of phase change forms the basis for thermodynamics. How materials exist as solids, liquids, and vapors and co-exist are a locus of all equilibrium states of materials. This exercise will familiarize you with pressure measurements. The three parts of this kit will culminate in a P-V-T diagram of an ideal gas.

A Verticle U-Tube Manometer

The Vertical U-Tube Manometer is an inexpensive and common differential pressure measurement device. A clear tube is bent into a U shape and 1/2 filled with a liquid of known density. One end of the tube is connected to an area of unknown pressure and the other end left open to the atmosphere or connected an area where the pressure is known.

Figure 1
A verticle u-tube manometer

The pressure difference measured can be calculated as:

$P_d = \rho gh$

Equation 1
P_d = Pressure(Pa); ρ = Density of the liquid in the U-Tube (water 997 kg/m³) ;
g = Acceleration of gravity (9.81 m/s²); h = Height of the liquid (m)

Setting up a Pressure Sensor

For the purposes of this lab, we are using a Honeywell SSCSNBN005PDAC5 pressure sensor. The name tells us a lot about the type of pressure sensor we are using. SSC means that the pressure sensor is standard accuracy, compensated/amplified. The S tells us that it is a single inline pin sensor. The NB tells us that it is a specific type of sensor with two ports. The N tells us that it only operates using dry gases (meaning you should probably not get any water into the sensor). The 005PD tells us that the differential pressure range for the sensor is ±5 psi (±34473.8 Pa). The AC tells us that it outputs an analog signal using a specific transfer function. The 5 tells us that it works with 5V. For the purposes of this experiment, it's also good to know that the accuracy of this sensor is ±2%. For more information regarding this pressure sensor and other pressure sensors, check out the datasheet for this sensor.

Insert the pressure sensor into the breadboard. Wire it up according to Figure 4. Connect the tubing provided to the bottom port. Important: This is a differential (+/- 5psi) sensor meaning it compares one port to the other. If both ports are at the same pressure the output voltage should be nominally half the supply voltage (in this case 4.8 volts). + 5psi = 4.8 volts and – 5psi = 0 volts. Exhale into the tube to measure your Maximum Expiratory Pressure (MEP). Inhale to measure your Maximum Inspiratory Pressure (MIP). Record the output voltages using your multimeter. Measure at least 5 intermediate pressures as well.

Figure 2

NOTE: The output type is analog.

Exhale into the tube to measure your maximum expiratory pressure (MEP). Inhale to measure your maximum inspiratory pressure (MIP). Record the output voltages using your multimeter. Measure at least 5 times.

$P_{app} = P_{min} + \frac{P_{max} - P_{min}}{0.8} \times (\frac{V_{out}}{V^{+}} - 0.1)$

Equation 2
P_max = +34473.8 Pa; P_min = -34473.8 Pa; V⁺ = 4.8V; V_out = sensor output voltage;
P_app = pressure difference detected

Use your Photon to Measure Pressure

Pin 2 of the sensor connects to the 4.8 volt supply of your Photon (pin labeled VIN). Pin 4 of the sensor connects to Ground. The output from the pressure sensor (pin 3) is ranging from 0-4.8V, but the photon only measures up to 3.3V. So build a voltage divider using two resistors (with resistance no smaller than 1kΩ). Connect the junction of the two resistors to AI0 of your Photon. Run the program pressureSensor.m and plot the data. How does the data you took by hand compare with the Photon data?

Notes on Constructing the Circuit

Using Multimeter to Measure Pressure:

Connect the tube to the inlet of the pressure sensor.

Figure 3 Pressure sensor

Insert all four pins into the breadboard.
Set the multimeter to 20V.
Note that the output voltage is an analog signal. So connect pin 2 with the Vin from photon (5V); connect pin 4 with the GND from photon; pin 3 outputs the voltage signal based on the pressure input into the sensor which you are going to measure. So connect pin 3 with the red probe of the multimeter (mAVΩ). You also need to connect the black probe of the multimeter (COM) to the GND from photon as well. Don't connect pin 1 to anything. Now the multimeter should display the voltage output by the pressure sensor.

Figure 4 Use multimeter to measure the pressure

Figure 5 Use multimeter to measure the pressure (2)

Using Photon To Measure the Pressure

You still need to connect pin 2 with the VIN and pin 4 with GND. Now you also need to use photon to measure the voltage output from pin 3. The Photon can only measure voltage within 3.3V, so you need to build a voltage divider. You can use two 10KΩ resistors to divide the voltage by half.
Now connect pin 3 with to one of the resistors, say R1. Connect R1 and R2. Then connect R2 with the GND. You need to measure the voltage on R2, so connect the junction of R1 and R2 with an analog pin from photon. In this way, you can sample the voltage signal and use MATLAB to process the data.

Figure 6 Use photon to measure the pressure