MODULE V Electrical engineering - Basics Page 53

11. Practical examples

In the table below some practical examples are given so that the service technicians can better understand with what kind of electrotechnical problems they will most likely be confronted at their place of work. Equipped with the basic electrotechnical knowledge this module intends to provide and with some additional practical training the technicians should be able to recognise the presented as well as other similar problems and should furthermore be able to solve them on their own. Corresponding practical training should especially focus on the following three areas:

• Plug and socket connection types (especially: connecting cables)
  
  
• Conduct measurements with the duspol and with multi-function testing devices
  
  
• Detect, repair and document faults in electric devices and installations with an unspecified amount of circuits

The exemplary problems presented in the table relate to a gas burner system since such devices are very frequently installed in heating systems and are also very often used to heat water.

Example	Possible causes for the defect and ways to correct it
The control display of the exhaust temperature safety limiter indicates a defect.	Cables and cable connections of the exhaust temperature safety limiter have to be checked.
	With a corresponding measuring device the exhaust temperature safety limiter has to be examined if it still conducts current. If no electricity flow can be measured, the exhaust temperature safety limiter has to be replaced
	The function of the circulation pump has to be examined. Cables and cable connections of the circulation pump have to be checked. Conduct a voltage measurement in the pump connection box. Mostly however, such a defect has a mechanical and not an electrical cause. In this case, the whole installation has to be disconnected from its power supply and then the pump has to be replaced according to the corresponding maintenance/service instructions.
	The cables and cable connections of the burner automatic (regulation and control device) have to be checked. Correct possible contact faults and replace defective cables.
	If all the repair efforts are not successful, the regulation and control unit is most likely defective and has to be replaced.
The security sensor indicates that the temperature is too high.	The cables and cable connections of the security sensor have to be checked.
	Control the resistance of the sensor with a corresponding measuring device. Depending on the temperature that can be measured (with a "seconds thermometer") at a certain distance to the sensor, the sensor must comply with manufacturer defined reference resistance values []. If the sensor does not comply with these reference values, it is most likely defective and needs to be replaced.
A too high temperature difference between the security sensor and the forerun sensor is indicated.	The cables and cable connections of the security sensor and the forerun sensor have to be checked.
	If necessary contact failures have to be eliminated and defective cables have to be replaced.
	Control the resistance of the sensor with a corresponding measuring device. Depending on the temperature that can be measured (with a "seconds thermometer") at a certain distance to the sensor, the sensor must comply with manufacturer defined reference resistance values []. If the sensor does not comply with these reference values, it is most likely defective and needs to be replaced.
A too high temperature difference between the forerun sensor and the reverse running sensor is being indicated.	The cables and cable connections of the forerun sensor and the reverse running sensor have to be checked.
	If necessary contact failures have to be eliminated and defective cables have to be replaced.
	Control the resistance of the sensor with a corresponding measuring device. Depending on the temperature that can be measured (with a "seconds thermometer") at a certain distance to the sensor, the sensor must comply with manufacturer defined reference resistance values []. If the sensor does not comply with these reference values, it is most likely defective and needs to be replaced.
The differential pressure switch does not close within the foreseen time.	Check the function of the blower.
	The cables and cable connections of the blower have to be checked.
	Check the fuse of the blower.
	Check the blower transformer with a corresponding measuring instrument. Very often 24V-direct current-transformers are being used (this can be looked up in the manufacturer documentation). If the necessary voltage is connected, the transformer has to work. If this is not the case, the transformer has to be replaced.
	If the blower is a 230V-blower, then the transformer can not be the cause for the defect and the blower itself has to be replaced.
	If the differential pressure switch still does not close correctly then most likely there is an electronic failure in the regulation and control unit and the unit has to be replaced.
The burner thermostat is indicating a defect.	The cables and cable connections of the burner thermostat have to be checked.
	If necessary, contact failures have to be eliminated and defective cables have to be replaced.
	The fuse of the burner thermostat has to be checked and replaced if necessary.
	Check the burner thermostat with a corresponding measuring instrument if it still conducts electricity. If it does not, the burner thermostat is defective and needs to be replaced.
	If the defect should still be indicated, then the regulation and control unit is defective and needs to be replaced.