Figure 1: Examples of heat If an equal amount of heat is added to each object, they will both increase in temperature. Figure 2: Increases in temperature The smaller brake disc will end up hotter than the engine block, even though they have both received the same amount of heat. The temperature, or the intensity of heat, is higher in the brake disc. It will feel hotter than the cylinder block. Automotive technicians need to measure temperature, to decide if systems are working correctly. Figure 3: Measuring temperatures in systems Safety First Measuring temperature can be DANGEROUS! don’t hot objects or liquids hot can burn your skin hot liquids can splash and burn your face and eyes. Always wear suitable Personal Protective Equipment for the job, such as face mask or safety glasses, and skin protection like gloves and overalls. Figure 4: Worker with safety equipment Temperature scales Temperature is measured on a scale based on two common effects of temperature: the freezing temperature of water the boiling temperature of water. Celsius temperature scale The Celsius temperature scale is divided into 100 parts between 0 and 100. Each section is called a degree. the freezing point of water is called 0 degrees, or 0o C.
The measurements could include engine oil pressure, transmission oil pressure, tyre pressure, workshop air line pressure, and manifold pressure. Choose the most suitable pressure gauge/s from those available in the workshop for each tasks. Connect to each system and record the pressure, including the units of pressure. An example has been done for you. System Type of gauge used Pressure Air in the workshop air line system Conventional pressure gauge 750 kPa Ask your trainer to check your results before proceeding. Trainer Signature: ................................................ Date: ...........................
Electrical quantities - what can we measure? There are many electrical quantities that can be measured. This resource will deal with only the important basics. Summary of electrical quantities Quantity Unit (used in Symbol (used in equations & Measured with: Voltage volt (V) V (or E) voltmeter Current amperes or ‘amps’ (A) A (or I) amp meter Resistance Ohms Ω (Greek letter, omega) R Basic electrical circuits There are two basic automotive circuits: series parallel. Parallel circuits A parallel circuit is a circuit in which the current has more than one current path. Figure 43: Parallel circuit Measure
Series circuits In a series circuit, the current flowing in the circuit has only one path to follow. The current must pass through all the components (the globes in this example) and connecting wires by one path only. In this circuit if one of the globes becomes open (burns out) the other globe will also go out. Figure 44: Series circuit In this type of circuit if one globe fails (becomes open) the other globe will remain alight. Series-parallel circuit A series-parallel circuit is a combination of a series circuit and parallel circuit. Some circuit components are wired in series and some are in parallel. In automotive electrical systems, a combination of these simple circuits are used to produce more complex networks. Figure 45: Series parallel circuit Activity 6 Question 1 Tick the correct answer. An electrical circuit is: a long line of electrical parts joined together by 18 watt light globes. an arrangement of components and wires that allows an electric current to flow. a mixture of wires and semi-autonomous batteries intersecting with a medium-sized flux capacitor. a circular device with components attached at 90o intervals. It may or may not include a battery. Question 2 Match these electrical circuit types with the illustrations, by drawing lines between matching pairs.
(sparks) away from the battery at all times. that can result in serious injury. Battery acid can cause severe injury to skin and eyes, and ruin clothes. Remove jewellery, including watches and rings. Metal jewellery is a good conductor of current; this makes it dangerous. Current passing through a metal watchband or ring may cause a severe burn. Report any unsafe conditions to your trainer. If you are in doubt about any system or procedure always seek help and advice from your trainer. Figure 47: Wear correct PPE Figure 48: No jewellery Vehicle and equipment safety Always refer to relevant service manuals for correct service procedures. Use only the test equipment specified. Avoid arcing (sparking) of components and connections as this may damage sensitive electronic components. Make sure that ignition is turned off before disconnecting or connecting battery cables. Use only the correct, specified fuses. Replacing a fuse with one of a larger capacity than specified may cause damage, or a fire! Pay strict attention to the polarity (positive & negative) of the battery and all components. Figure 49: Read safety signs
Selector Switch This rotary switch selects the function, and desired range. Power Switch Switch turns meter on or off. (sometimes on the rotary switch) DC/AC Switch Selects DC or AC voltage or current. DC is the setting used for most automotive work. (sometimes selected with the range switch) To measure voltage, use the COM and VΩ Hz sockets. Sockets used to measure voltage To measure current up to 200mA (200 milliamps), use the COM and µA mA sockets. Sockets used to measure current up to 200A
This page has been left blank intentionally Glossary WORD MEANING anchored Connected to something which doesn’t move arcing Sparking when an electric current between two points separated by a small gap atmospheric pressure The pressure of the air all around us, measured at sea level Also called ‘air pressure’ audible You can hear it bulb Round section at the bottom of a thermometer calibrate, calibration Set the start point of the measuring scale Make sure the gradations on a measuring device are accurate circular (say “serk- ye-lar”) Round
probe Touch Place tip inside or near to measure pulsate (also see vibrate) Change rapidly backwards and forwards between two points range (of a scale) From lowest point on the scale to the highest point on the scale resistance The force in a circuit that resists or restricts current flow restrict Limit, partly close robust Strong, not easily breakable rotate Turn sense Feel similar Almost the same spiral See coil stabilise Stop moving, reach its final state substance Material symbol A single sign or letter that stand for a bigger name transfer Move toxic Poisonous vacuum (say “vak-yem”) A space with no air inside it; or less air than at normal atmospheric pressure vibrate (also see pulsate) Move rapidly to and fro voltage The electrical pressure or force in a circuit