Data Acquisition and Auto Lab Report
purpose
· Interface the DAQ Chassis with photoresistors
· Interface pressure and vibration sensors with the cDAQ chassis
· Understand the basic operation of pressure and vibration sensors
Application
· Automated street lights
· Automated home lights
· Alarm systems
· Stability control systems
· Earthquake detection
Introduction
Since we are living the era of technology, we are living in a world of sensors too. Different types of Sensors could be found in our homes, offices, cars etc. working to make our lives easier by turning on the lights by detecting our presence, adjusting the room temperature, detect smoke or fire, make us delicious coffee, open garage doors as soon as our car is near the door and many other tasks. All these and many other automation tasks are possible because of Sensors.
Sensor is a device that when exposed to a physical phenomenon (temperature, displacement, force, etc.) produces a proportional output signal (electrical, mechanical, magnetic, etc.). The term transducer is often used synonymously with sensors. However, ideally, a sensor is a device that responds to a change in the physical phenomenon. On the other hand, a transducer is a device that converts one form of energy into another form of energy. Sensors are transducers when they sense one form of energy input and output in a different form of energy. For example, a thermocouple responds to a temperature change (thermal energy) and outputs a proportional change in electromotive force (electrical energy). Therefore, a thermocouple can be called a sensor and or transducer.
Light Sensors
Light Sensors are photoelectric devices that convert light energy (photons) whether visible or infra-red light into an electrical (electrons) signal. A Light Sensor generates an output signal indicating the intensity of light by measuring the radiant energy that exists in a very narrow range of frequencies basically called “light”, and which ranges in frequency from “Infra-red” to “Visible” up to “Ultraviolet” light spectrum.
The light sensor is a passive devices that convert this “light energy” whether visible or in the infra-red parts of the spectrum into an electrical signal output. Light sensors are more commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons).
Photoelectric devices can be grouped into two main categories, those which generate electricity when illuminated, such as Photo-voltaics or Photo-emissives etc, and those which change their electrical properties in some way such as Photo-resistors or Photo-conductors. This leads to the following classification of devices.
• Photo-emissive Cells – These are photodevices which release free electrons from a light sensitive material such as caesium when struck by a photon of sufficient energy. The amount of energy the photons have depends on the frequency of the light and the higher the frequency, the more energy the photons have converting light energy into electrical energy.
• Photo-conductive Cells – These photodevices vary their electrical resistance when subjected to light. Photoconductivity results from light hitting a semiconductor material which controls the current flow through it. Thus, more light increase the current for a given applied voltage. The most common photoconductive material is Cadmium Sulphide used in LDR photocells.
• Photo-voltaic Cells – These photodevices generate an emf in proportion to the radiant light energy received and is similar in effect to photoconductivity. Light energy falls on to two semiconductor materials sandwiched together creating a voltage of approximately 0.5V. The most common photovoltaic material is Selenium used in solar cells.
• Photo-junction Devices – These photodevices are mainly true semiconductor devices such as the photodiode or phototransistor which use light to control the flow of electrons and holes across their PN-junction. Photojunction devices are specifically designed for detector application and light penetration with their spectral response tuned to the wavelength of incident light.
Experiment
Exercise 1:
In this exercise we will construct a photoresistor circuit and connect it to the cDAQ chassis. By using a photoresistor sensor and 1K ohm resister we built the following circuit (figure 1).
For the simulation part, we create a circuit consists of two DAQ assistant analog, voltage type. One of them input connected to data indicator. And the other is output, connected to a data control (figure 2).
The results show, a higher voltage was produced when we focus the light on the sensor. The highest voltage obtained was 1.28 V, while the lowest was 0.51 V (figures 3 and 4).
Regarding to the resistance of the photoresistor, the reading shows, the maximum resistance was obtained during the darkness mode, 79.3K ohm. While the detected minimum resistance was 2.77K ohm, which was obtained in the light mode (figure 5).
Exercise 2:
One of most common applications for photoresistors is home lights automation. This exercise will simulate that experience using the components available in the lab. Using your knowledge of photoresistors develop a VI, that turns on LEDs when the light level drops below a certain threshold.
In this exercise the photoresistor circuit remain the same, we just update the LabVIEW circuit. To obtain our goal, we add a less than operation, comparing between the output voltage with a very low voltage (light off voltage). On the other side it connected to a Boolean LED.
If the obtained voltage detects to be dark the light will be ON otherwise the light will be Off.
Exercise 3:
In this exercise we should construct a circuit using the pressure sensor and connect it to the cDAQ chassis. For the physical connection we replaced the photosensor with the pressure sensor as shown in (figure 9).
For the LabVIEW both Block Diagram and Front Panel, nothing changed, the first exercise settings are used here also.
The results show applying a pressure on the pressure sensor will obtain the maximum voltage, which was 1.8 V. while releasing the sensor without any pressure will obtain the minimum voltage which almost equal 0 V.
Regarding to the resistance readings of the pressure resistor, the maximum resistance was so high that can be considered as infinity, and this result obtained when no pressure applied on the sensor. While the minimum resistance was which obtained after applying a pressure on the sensor.
Exercise 4:
First we going to answer this How does a piezo buzzer operate? The buzzer contains an electromagnetic coil that vibrates a small diaphragm. The interface circuit uses an NPN transistor as a switch to turn the coil current on and off and a diode to protect the transistor from large back-emf voltage when the transistor abruptly shuts off the coil current.
Secondly the discretion of exercise four, we used a passive buzzer (also called a magnetic transducer) generates tones over much of the audible frequency spectrum, it is controlled by a digital signal of varying frequencies. Additionally, we used 9263 module to get a digital output. We connected the circuit in the breadboard like figure (1)
For software part we created a new VI labView then we added some component to end up with figure (2):
We insert DAQ assistant to generate voltage analog output. We did set the generation mode to sample on demand. Then we added another DAQ assistant, in order to generate a voltage analog output, we set the generation mode of this one to N Samples. Then we added a Simulate Signal box to the block diagram and change it to a square wave. In addition we added controls for amplitude, frequency and offset. We did change the text box for frequency to a slider with a range from 0-5000. Then we added a constant control for DAQ Assistant with a value of 5 and connect Simulate Signal to DAQ Assistant 2. After we finished from all these steps then we test our design works then we listen to the sound after we drag the slider on the frequency controller.
