07-04-2008, 08:53 PM
Ah ha, the "ballast resistance calculation" dilemma. Probably one of the most common things that people make a mistake on, and the bit that we did right at the end of tonight's study group.
Remember that the ballast resistance is effectively made up of loads of resistors in parallel, so if the TC is longer, the total will be smaller. The value for ballast resistance is quoted in the units of "ohm km" and here as a value of 2.5 ohm km. This means "the length of the tc in km times the resultant equivalent value of resistance must be 2.5", hence the formula given is correct but appears odd at first sight.
Thanks for asking the question, it shows someone is thinking about things.
You are never wrong, but there may be some things that you have not quite had the chance to learn properly yet.
P.S. For resistance read "impedance" to be fully correct and not lazy like me.
Remember that the ballast resistance is effectively made up of loads of resistors in parallel, so if the TC is longer, the total will be smaller. The value for ballast resistance is quoted in the units of "ohm km" and here as a value of 2.5 ohm km. This means "the length of the tc in km times the resultant equivalent value of resistance must be 2.5", hence the formula given is correct but appears odd at first sight.
Thanks for asking the question, it shows someone is thinking about things.
You are never wrong, but there may be some things that you have not quite had the chance to learn properly yet.
P.S. For resistance read "impedance" to be fully correct and not lazy like me.