Thursday, July 1, 2010

Control Valve

The last week of my training, I'd learned about he structure of the control valve. There are 2 types of valves in general: ON/OFF valve and Control valve. The difference between the two is that the ON/OFF valve can only be open or close, while for the control valve, the user can decide how many percent they want the valve to be opened.

The control valve is controlled by the power supply from the range of 4mA-20mA, which represents:
4mA - 0%
8mA - 25%
12mA - 50%
16mA - 75%
20mA - 100%

On a control valve, there were 2 inputs and 2 outputs. The 2 inputs refer to the pressure supply and the power supply. The 2 outputs is main to open and close the valve. 1 output is use to open the valve and another is used to close the valve. Below are the operation of a control valve.

A constant pressure inject to the positioner of the valve. The positioner will refer to the power supply (control variables) to it. If the supply is 4mA, then the positioner will gives an instruction and transfer the pressure into the output to close the valve. On the other hand, if the power supply received is 12mA, which gives an instruction to open the valve 50%, then the positioner will inject the pressure into the output where used to open the valve and stop opening the valve when it reach 50%.

Sunday, June 20, 2010

AC Drives troubleshooting

Basically this week, I'm helping one of the supervisor in the instrument department, Mr. Lee Yoon Kian to troubleshoot the AC Drives. The AC Drives that are malfunction will be sent to the instrument calibration room for maintenance.

First of all, Mr. Lee checked all the I/O control cards in the AC drives to make sure that all the I/O control cards are good in condition. If the cards were burnt, the new I/O card will be replaced. If the cards are OK, then Mr. Lee will proceed to the next steps. He will start checking the IC on the control card. In some cases, the control card is OK, but the problem happen on the IC on the board, which may be burnt or spoiled, result the control card couldn't function well and causing the malfunction of the AC drives.

If the problem still haven't detected after troubleshooting the control cards and ICs, he will start checking the parameters in the ICs. Due to some technical problems, sometimes the codes and the parameters in the IC will be imprecise and incompatible with the motors and drives. So the new parameters have to be re-uploaded into the IC using the DMS software, a software used to download or upload parameters from/to the IC.

Until here, if the problem still couldn't be identified, he will check the chopper part and the transformer in the AC drives. The capacitor banks in the chopper will be opened up to determine whether the capacitor banks are still functionable or whether the terminal + and — are connected in the right manner, or the types of capacitor banks is correct (Ex: 15µF). To make sure every steps he performed are correct, he usually accompany a user manual with him because the AC Drives use a very high voltage and power. It will be dreadful if anythings go wrong~

Super Juni-or ji~