Measuring Refrigerant Gases Sound Speed Using Arduino and App Inventor 2
Introduction: Measuring Refrigerant Gases Sound Speed Using Arduino and App Inventor 2
The purpose of this Instructable is to build a portable device that can measure the speed of sound in refrigerant gases and use this data to identify them.
The speed of sound in an ideal gas is related to two characteristics of the gaseous substance, its molecular mass (kg/mol) and its adiabatic constant (heat capacity ratio), or its average values in case of being a mixture of gases.
It is for this reason that the measurement of the speed of sound can be used as a preliminary way to identify a pure gas or mixture of gaseous substances.
The measurement can be performed using an ultrasonic proximity sensor, to measure the round trip time ( t/2 ) of a sonic pulse in a plastic tube of known length ( x ) (echo method), filled with the gas under study ( v = 2x/t ).
Since the speed of sound is also absolute temperature dependent, it must be measured using a digital temperature sensor.
The values measured by the sensors are captured and processed by an Arduino microcontroller that transmits them via bluetooth to a mobile application, designed with App Inventor 2, which will allow to calibrate the length of the plastic tube using a reference gas whose sound speed is known.
The application will use this information to calculate the sound speed of an unknown sample of a refrigerant gas and perform preliminary identification (see disclaimer **).
Supplies
* PVC pipe piece approximately 14 cm long and 4.8 cm in external diameter (1-1/2'').
* 2 PVC pipe caps approximately 4.8 cm in internal diameter (1-1/2'').
* 2 Toothpaste tube shoulder pressure caps.
* 1 Piece of leak repair tape about 15 cm x 25 cm.
* Epoxy glue.
* 1 Plastic container.
* 1 Breadbord.
* 1 Arduino Nano V3.0 CH340 with mini usb cable.
* 1 HC-SR04 ultrasonic sensor.
* 1 TMP36 digital temperature sensor.
* 1 Bluetooth HC-06.
* 1 1k ohm resistance.
* 1 2k ohm resistance,
* Male/male jumpers cable.
* Male/Female jumpers cable.
* 1 Male/female usb cable.
* 1 Portable battery charger (6000 mAh 3.7V, Out 5V, Output Max. 2.4A)
* Electric tape.
* Velcro tape.
Step 1: Measuring Probe
The measuring probe is basically a piece of PVC pipe approximately 14 cm long by 4.8 cm external diameter (1-1/2'') to which three holes are drilled, two for gas inlet and outlet (provided with pressure caps of the type used in toothpaste tubes) and another for inserting a digital thermometer.
This pipe will be closed at its ends by two PVC pipe caps approximately 4.8 cm internal diameter (1-1/2''). One of the caps will have two perforations to accommodate the emitter and detector of the ultrasonic sensor. This part of the device is going to be the point of emission and detection of ultrasonic pulses, while the flat face of the other cap, opposite the emission point will be the rebound point (echo) of the pulses.
The following is the procedure for constructing the measuring probe:
* From a 1-1/2'' PVC pipe cut a piece about 14 cm long.
* About 4 cm from each end of the tube piece make two perforations, in opposite directions, approximately 5 mm in diameter.
* On the perforations made paste with epoxy resin the two pressure caps of toothpaste tubes.
* Halfway through the tube and perpendicular to the plane formed by the two holes described above open a hole about 1 cm in diameter.
* Through the above hole insert the temperature sensor TMP36, attached to its connecting cables and with the help of electrical tape stick to the upper inner wall of the PVC tube leaving exposed the sensor head. 152
Fix externally with epoxy glue.
* Make two perforations approximately 1.5 cm in diameter separated by 2.5 cm to one of the PVC pipe caps so that they adjust the emitter and receiver of the ultrasonic sensor HC-SR04 and that are centered on the face of the cap. Fix the HC-SR04 sensor with expoxi glue making sure to seal all slots. Let the glue dry.
* Place the cap with the ultrasonic sensor and the cap that will function as a rebound surface, at the ends of the tube (measurement probe). Coat the rest of the exposed externas surface of the tube with leak repair tape so that it is thermally insulated. 320