Sensing & Measuring
The ability to sense various physical features of the environment and also to monitor them quantitatively is a unique feature of electronic products.
| Understanding Technical Function - Sensing and Measuring |
| Introducing |
- Know that a wide range of environmental signals can be sensed using electronic components (sensors) including temperature, light, moisture, sound, pressure, force, magnetism, movement/angle
- Know that some sensors are switches (being either off or on)
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| Developing |
- Understand that switching sensors provide a digital signal (high or low voltage)
- Know that many sensors respond to environmental signals by varying their resistance or produce a changing voltage
- Sensors whose resistance varies provide an analogue signal; where the value varies between 0V and the supply voltage
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| Enhancing |
- Understand that where sensors provide a changing resistance, a potential divider is used to convert this change into a varying signal (voltage) that depends on the ratio of the two resistances in the potential divider
- Be able to use the potential divider equation to select appropriate resistors for a particular sensor
- Understand that many electronic components only accept digital signals, so analogue signals may have to be converted into digital signals (analogue-to-digital conversion - ADC)
- Be able to use a comparator for simple ADC. Understand that this provides a high signal when the input is above a certain threshold and a low signal when the input is below that threshold
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| Advancing |
- Understand matched pairs of IR or ultrasound emitters and receivers can be used to sense proximity and that light or IR sensors can sense surface colour.
- Know that pulses in digital signals can be counted electronically.
- Know that mechanical switches produce multiple pulses when pressed due to ‘switch bounce’ and that this needs to be accounted for in counting circuits either with a ‘de-bounce’ circuit or in a counting program.
- Know that the rate at which pulses arrive at a sensor can be measured as a frequency.
- Understand that a comparator provides one-bit ADC in which most of the information about the input signal is lost.
- Using multiple threshold values for digitisation allows more of the information in an analogue signal, to be preserved.
- Understand that each ADC threshold adds an input signal; e.g. 4 thresholds lead to 4 digital signals representing the value of the original analogue signal. Know that ADC chips are used for this.
- Understand that measurement often requires complex signal conditioning, as most sensors don’t respond linearly to changing conditions. Some sensing devices provide measurement signal conditioning within an IC and therefore do give a linear response
Know that a wide range of modern electronic devices provide access to sense and measurement data that are relatively novel. These include location data from GPS and GIS systems, RFID data, data from accelerometers and internet based data
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