mzansijobs

PROGRAMMABLE LOGIC CONTROLLER (PLC) This is Omron type of PLC used in the equipment enclosures. I have managed to program this PLC before doing function testing. The main programme is entitled to safety with respect to point machines, and train detection monitored on the LCP (Local Control Point). LOADING PROGRAM I plugged the USB cable to the computer and PLC. I opened the Omron PLC progrmme and wait for about 30 seconds for the respond. The screen shown below popped up and I selected object ID to change the binary value using the last two decimal values of the IP address on the equipment enclosure. Each equipment enclosure has a unique ID and function to the points being controlled and the track being monitored.   Since these enclosures were monitored by LCP, the communication between the two was carried by the Ethernet switch. Each PLC had its unique IP address this is used by the switch to identify eac...

BOLOMETER POWER SUPPLY CIRCUIT DISCRIPTION The circuitry provides power to the bolometer. It drives its DC voltage from the transformer T1 and the diode bridge D7. The smoothing of the supply is done by the capacitor C13. Varistor RV2 provides transient protection. The circuitry consists of U4 a switched mode power supply integrated circuit. It is configured in the step down mode of control. L2 is charged when the internal transistor is turned on. During the off cycle diode D4 is conducting and the energy stored in L1 is transferred into the capacitor C8, C8 maintains the average output voltage. Resistor R7 and R9 provides the feedback voltage to control the on/off duty cycle. TESTING I did visual inspection by checking transformer T1 connection for correctness. The primary winding is on the left of the connector T1 as shown by the two wires on the photograph above. The secondary winding is on the right of T1 a...

BOLOMETER SENSOR GENERAL DISCRIPTION This device senses the temperature difference between its environment (ambient temperature) and any object passed in front of its lens. The focus distance of the bolometer is approximately one meter (1m).The output of the sensor   is an open-collector type and must be pulled high to 24V with a 4.7KΩ resistor to see voltage output. FAULT REPAIR With the help of the schematic diagram shown below I have managed to trace and repair faults on the bolometer sensor. The schematic diagram shows the expected values at every test point so I had to check if the values labeled correspond on the PC board. The steps below describes how   I carried the test.   I connected the bolometer to the cable plug. I turned on the power to the bolometer I measured the 24V supply voltage (the voltage should be between 23.5V and 24.5V. I measured the +175V and -175V supplies to the bolometer this was done on the test rig. With the ...

RESISTORS Resistors are identified on a circuit using numbers and colours (colour coding) to show the exact value of resistance. IDENTIFICATION   When I was populating PC Boards I have used SM resistors, they use numbering system for identification than colour coding. It can either be 3 or 4 digits, in case of 4 digits resistor like the one shown above the first 3 digits represent the 3 digits in the answer and the fourth digits represent the number of zeros to place after the 3 digits. The value of the resistor shown above in this case the value will be 15K Ω. In the schematic diagram the resistor is represented by a jagged line or margin and the value is always return next to the identifier e.g. R1 To reduce number of resistors in a circuit, a set of identical resistors is used called Single-In-Line (SIL) resistor network as shown above. USE A resistor is a small component designed to provide specific amount of resistance in an electronic circuit. The m...