Quiz on Sensors and Data Acquisition

Sensor Information for Questions 1-3: A temperature sensor gives an output of 4 mA at 275 K or below. Temperatures of 325 K and above give an output of 20 mA with a linear output between the lower and upper limits.

1. In terms of sensor terminology, how would you classify the lower temperature 275 K for this sensor?

A. Zero
Correct. The zero is the lowest value that can be detected by the sensor.
B. Span
Incorrect. The span is `325K - 275K = 50 K`.
C. Gain
Incorrect. The gain of the sensor is `K_m={20-4mA}/{325-275K}={16mA}/{50K}=0.32{mA}/{K}`
D. Freezing point
Incorrect. The freezing point of water is 273.15 K. The sensor is not classified by the freezing point of water.

2. What is the sensor gain?

A. 3.125 `{K}/{mA}`
Incorrect. This answer is the inverse of the gain `1/{K_m}={325-275K}/{20-4mA}=3.125`
B. 0.32 `{mA}/{K}`
Correct. The gain of the sensor is `K_m={20-4mA}/{325-275K}={16mA}/{50K}=0.32{mA}/{K}`
C. 275 K
Incorrect. This is the zero value
D. 16 mA
Incorrect. This is the range of the sensor output 20-4 mA = 16 mA

3. What is the expected sensor signal at a temperature of 276 K?

A. 0.32 mA
Incorrect. At 276 K, the sensor output increases by 0.32 mA above the starting value of 4 mA. The sensor output is always between 4 and 20 mA. Any lower value is an indication that the sensor is not working properly.
B. 4.32 mA
Correct. At 276 K, the sensor output increases by 0.32 mA above the starting value of 4 mA.
C. 5 mA
Incorrect. The output does not increase by 1 mA with a 1 K temperature increase, only 0.32 mA.
D. 36 mA
Incorrect. The sensor output should always be between 4 and 20 mA.

4. Which of the following is a difference between a Raspberry PI (micro-processor) and an Arduino Uno (micro-controller)

A. An Arduino allows data acquisition while a Pi does not
Incorrect. Both systems can read sensors. The Arduino and Raspberry Pi can read digital (0, low voltage or 1, high voltage) while the Arduino can also read analog (voltage) between 0 and 5 V with a 10-bit Analog to Digital Converter (ADC).
B. A Raspberry Pi can run Linux and other common operating systems
Correct. This is an important difference in the purposes of the devices.
C. Raspberry Pis can be used in automation
Incorrect. Both micro-processors and micro-controllers are useful in automation but mostly for prototype development. Industrial automation typically uses systems such as Programmable Logic Controllers (PLCs) or a Distributed Control System (DCS) that is built for reliable control. Raspberry Pis do have higher processing capabilities while an Arduino is better for real-time or high-speed sensing and control.
D. An Arduino has digital inputs for sensors
Incorrect. Raspberry Pis also have digital inputs. Arduinos have analog inputs, which Raspberry Pi does not have without adding an extra ADC chip.