Accuracy and quality control
When creating electrical or mechanical products, the accuracy of production is vital. If one part of the process is poorly fitted or too big, the products will not function and could become dangerous to the user. How accurate a product needs to be is described as the toleranceThe amount by which a measurement can vary without affecting the ability of the product to be manufactured accurately..
Poorly fitting mechanical parts will perform badly and are likely to have a very small tolerance measurement. For example, chains or gearA wheel with teeth that can change the speed of a mechanism. that are slightly bigger or smaller than necessary will be prone to jamming and breaking.
Printed circuit boards (PCBs) need to be so accurate that any tolerance measurements are likely to only be +/- 1 mm, to stop any materials touching and causing circuits to stop working.
resistorAn electrical component that restricts the flow of electrical charge. Fixed-value resistors do not change their resistance, but with variable resistors it is possible to vary the resistance. used in electrical circuits have a tolerance relating to the amount of power they allow into a circuit. The smaller that tolesrance is, the less likely the circuit is to be overloaded and damaged, but the more expensive the resistor will be. The amount of tolerance a resistor has is shown with the colour of the fourth stripe down and is usually silver or gold
Example
A resistor has a value of 1,500 Ω and has a tolerance of +/- 10 per cent.
1,500 × 0.1 = 150
Range of tolerance = 150 Ω either side of the 1,500 Ω mark.
1,500 Ω + 150 Ω = 1,350 Ω minimum
1,500 Ω - 150 Ω = 1,650 Ω maximum
Question
A resistor with a value of 22,000 Ω has a tolerance of +/- 5 per cent. What are the minimum and maximum values for this resistor?
22,000 × 0.05 = 1,100 either side of the 22,000 Ω mark.
22,000 - 1,100 = 20,900 Ω minimum
22,000 + 1,100 = 23,100 Ω maximum
Quality control
During the manufacturing process, quality control (QC)A set of checks intended to ensure that a product will meet the specified customer requirements once it has been manufactured. These procedures are followed before work is complete, as opposed to afterwards. (QC) checks are carried out. These can check whether:
- PCBs are cut accurately
- components are attached securely
- casings are attached securely
- edges on castings are trimmed and neat
Although quality control checks can increase waste with faulty products being thrown away, if a factory develops a reputation for being reliably high in quality, money is saved in the long term through products being reordered.
