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Section A Question Theme 2014

Section A Question Theme 2014. Temperature monitoring in a retail environment. Retail?. Drugs. Food in cafe. Plants. Temperature of shopping environment. Shop floor. Garden Centre. Pharmaceutical. Retail. Fresh flowers. Cold food. Supermarket. Bars & Restaurants. Fresh fruit/ veg.

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Section A Question Theme 2014

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  1. Section A Question Theme 2014 Temperature monitoring in a retail environment

  2. Retail? Drugs Food in cafe Plants Temperature of shopping environment Shop floor Garden Centre Pharmaceutical Retail Fresh flowers Cold food Supermarket Bars & Restaurants Fresh fruit/veg fridges Deli counters fish Hot food drinks freezers meat cooked Coffee machines Beer storage raw

  3. System Block

  4. Thermistors • Thermistor (the most common type)

  5. Transistor circuit - 1 LED and current limiting resistor Variable resistor and thermistor make a voltage divider. NPN transistor and base protection resistor The variable resistor sets the sensitivity, so you can ‘calibrate’ the circuit to operate at a specific temperature.

  6. Transistor circuit - 2 If you want a circuit that indicates temperature getting colder you need a voltage divider with the ntcthermistor in the bottom position: If you want a circuit that indicates temperature getting hotter you need a voltage divider with the ntcthermistor in the top position: Temp goes down, thermistor resistance goes up, more voltage developed onto transistor base, transistor turns on. Temp goes up, thermistor resistance goes down, more votage developed onto transistor base, transistor turns on.

  7. Operational Amplifier (Comparator) circuit Detecting rising temperature - thermistor at the top of a voltage divider. The potentiometer sets the sensitivity (in itself a voltage divider.) The comparator circuit compares the difference between the two inputs, and sends an output to the LED when there is a positive voltage difference. Thermistor and resistor make a voltage divider. LED and current limiting resistor Potentiometer Op-Amp with 2 inputs

  8. PIC circuit to detect high and low temperature points (program on next slide) Red and Green LED (with current limiting) and piezo sounder 5 volts Thermistor sensor connected to analogue input microcontroller outputs Analogueinput 0 volts Pull down resistor

  9. PIC flowchart program to detect high and low temperature points Start Analogue input - Over temperature? Yes Green LED off.Red LED & piezo sound on. No Green LED on.Red LED & piezo off. Analogue input - Under temperature? Yes Green LED off.Red LED & piezo sound on. No Green LED onRed LED & piezo off.

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