Question

Please answer me short to the point (not longer than one sentence. If possible, answer me in words.

1)How does a VFD ( Variable Frequency Drive) provide frequencies that are different from the incoming line frequency?

2) In VFD (Variable Frequency Drive), the stop button needed to be wired as normally closed while the forward and reverse start buttons were normally opened. Why are they different? Why not make the stop button normally opened too?

3) What type of conveying system would be best inside an oven and allow for airflow thru the belt?

4) What is the term that identifies that the conveyer drive mechanism is separate from te items being conveyed? In other words, the loads are asynchronous and do not necessarily move at the same time.

5) How could overloads tripping or fuses blowing be caused by poor tracking of the conveyor belt?

Answer 1

1)The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.

2)Some of you noticed that in order to make this example follow good practice, I should use a normally open contact in the ladder logic, and a normally closed contact as input actuator. By doing so, the input will be not produce hazardous situations under failure. Important when it comes to the risk assessment process. The same is also true with safety relays and contacts in safety circuits.

3)

CONTINUOUS AIRFLOW STYLES

There are five (5) standard types of airflows used in conveyor ovens: Top-Down, Bottom-Up, Top & Bottom, Horizontal, and Combination. Horizontal and Combination airflow are least common in conveyor ovens, but are used in batch ovens quite often.

5)But it is also important that you understand why the breaker has tripped or the fuse has blown to avoid having it happen again. In rare cases, the breaker may be damaged and need replacing. But in most cases, the breaker or fuse is just doing its job when it pops. Circuit breakers are designed to trip and fuses are designed to blow and turn off the power when any of four dangerous situations occur.

a)Overloaded

b)Short Circuit

c)Ground Fault

d)Arc Fault