Surge Arrestor based on Quarter wave shorting stub

This technology is based on quarter wave transformation line.
The coaxial shorting stub applied for this purpose is short circuited at its end and its length is matched to the mid-band frequency of the operation band.It threby forms a band-pass filter.
Since lightning interference have a low frequency spectrum the shorting stub act as a short circuit, conducting the current to ground.

In regular operation, the RF signal reaches the entry of the shorting stub (shown here as point 1).
It then runs along the shorting stub up to the short (point 2). This corresponds to a 90° phase shift.
 At the short, the signal is reflected (point 2') –a sudden phase shift of 180° is created – and flows back to the start of the shorting stub (point 1'), where it arrives after another 90° phase shift.

As a result, the reflected signal is again in phase with the arriving signal. Therefore, the RF signal does not detect the short.

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Surge Arrestor based on High Pass Filter

The concept behind this filter is that the low-frequency components of the lightning surge gets shunted to ground. As lightning energy has low frequency (lesser than 100KHz), these SA works as a high pass filter blocking surge energy.

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Surge Arrestor based on GDT Principle

Depends on the working of Gas Discharge Tube.

A gas tube is an over voltage device that shunts current when a threshold voltage (the spark-over voltage) is reached. These are typically rated from 90V to 600V. It contains ionized gases.

When a voltage disturbance reaches the GDT sparkover value, the GDT practically shorts the line, diverting the surge current through the GDT to ground.

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BASIC PRINCIPLE FOR RF SURGE ARRESTOR

There are basically three principles for coaxial SA devices.
Component based
1. Gas dischage tube (spark gap) Click here to know more about this principle
Filter based
2. High pass filter Click here to know more about this principle
3. Quarter wave shorting stub (Band pass filter) Click here to know more about this principle

Besides of these three, Designer uses Hybrid technolgy which combine two principles from above for its desired working.

RF Surge Arrestor

SA is a device to protect electrical equipment from over voltage transients caused by external (lightning) or internal (switching) events.

Concept behind Protection - Shunting

The goal of these devices is to protect the end product by shunting energy away. When the protection devices turn on, their impedance are reduced substantially. The circuit becomes current divider with most current going through the protection device.

Major Categories of RF Surge Protection Devices

1. Circuit Protection Components

Most common method of shunting transient energy is through circuit protection components such as Gas Tubes.

2. Filtering Components

Major method of shunting transient energy is through filter components such as inductors and capacitors.

Filter based RF SA's would have inductors and capacitors designed to handle kiloamp levels of surge.

To know on what principle these RF Surge Arrestor please click here.Basic Principle for RF Surge Arrestor

Interview Questions For Quality Engineer/Manager

Q1: Tell me something about yourself or your brief introduction.

Q2: Tell me about your present company.

Q3: What are your roles/ responsibilities in your present organisation.

Q4: What are your day to day's activities in your present organisation.

Q5: 7 QC tools

Q6: Who is responsible for handling customer complaints in your organisation? if you are responsible, how you handled the customer complaints?

Q7: What is 8D?

Q8: Different types of root cause analysis. give some example of using these method in your organisation.

Q9: What are your departmental goals?

Q10: Internal rejection rate or Internal DPPM, How you calculate & monitored?

Q11: Difference between correction & corrective actions.

Q12: What is/ are your achievement in your career?

Causes of Passive Intermodulation (PIM)

Ø Coaxial connectors - these connectors have joints between dissimilar metals and areas where oxidation can occur. Connectors that are assembled well using high quality components and water proofed well if they are to be used externally should last, but any connector will deteriorate with time. Connections made with poor connectors, or of the connectors have been assembled poorly will generate higher levels of PIM faster.

Ø Feeder lines - feeders such as coaxial feeders generate levels of passive intermodulation. The braid in the outer conductor provides many metallic interfaces in which passive intermodulation, PIM can be generated. Even if foil is used, there are interfaces between the layered construction of the foil wound round the dielectric. For applications where passive intermodulation is important coax with a good PIM performance can be bought. Some manufacturers may guarantee levels to below a given level, e.g. -140dBc, although at a cost.

Ø Joints where dissimilar metals meet and oxidation, etc. occurs converting the joint into an area that exhibits some diode effects.

Ø Dirty connections

Ø Loose connections and irregular contact areas, on a macroscopic or even a microscopic scale, can cause an inconsistent flow of current and generate inhomogeneous electromagnetic fields.

Ø General anodic effects

Ø The use of ferromagnetic metals, like iron, nickel and steel can give rise to passive intermodulation. These metals show magnetic hysteresis effects when energy is applied. This means that the resulting signal level is dependent, even to a small degree on input level. Hence this is a non-linear effect.

Ø Spark discharges can give rise to passive intermodulation. The spark will cause craters to be formed and some oxidation that will generate a diode effect. Sparks can result from poor connections or even the hot connection or disconnection of a connector.

Passive Intermodulation (PIM)

Passive intermodulation (PIM) is a form of intermodulation distortion that occurs in passive components such as antennas, cables, connectors, or duplexers with two or more high-power input signals. PIM in the transmission path degrades quality of the wireless communication system. Passive intermodulation occurs when two or more signals are present in a passive non-linear device or element. The signals will mix or multiply with each other to generate other signals that are related to the first ones.PIM can produce interference, and this can sometimes hide the wanted signal.

To know causes of PIM click on below link:
 Causes of Passive Intermodulation (PIM)

Difference among Correction, Corrective & Preventive actions

Mostly, all the professionals come across these words specially Quality professionals . But sometimes we confused with the actual meaning of all these three words. I will try to explain all these words one by one with an example;

Correction

Suppose your smart phone touch screen gets damaged by falling on ground. What will you do first, of course you will get replaced your damaged touch screen by new & working touch screen. This is called correction. In short “ Correction is the action to eliminate non-conformity or correcting a occurred problem”.

Corrective Actions 

Now, when you replaced your touch screen of your smart phone what will you do next so that you don’t need to replace your touch screen again. You install a tempered glass on your smart phone touch screen. This is called corrective action as you are safe guarding your smart phone touch screen. In the event of falling of your smart phone, your touchscreen will be safe on the cost of tempered glass. In short “ Corrective action are taken on the root cause of the problem in such a way that it should not occur again”.

Preventive Action 

When you are installing tempered glass on your smart phone touch screen, you also installed tempered glass on your wife smart phone to avoid any future damage to her smart phone touch screen. This is called preventive action. “Preventive action is like failure mode effect analysis (FMEA) or risk management, where the non-conformity or problem have not actually occurred. We need to anticipate the risks that may occur & than think of actions that shall eliminate the cause of non-conformity”.  

I hope this will clears the concept of Correction, Corrective & Preventive actions. If you have any doubt or question please leave a question in comment box.

TYPES OF SOLDER ANOMALIES/ DEFECTS

Following are the list of solder anomalies/ defects which we generally faced in soldering process:

1. Exposed Basis Metal

2. Pin Holes

3. Blow Holes

4. Non - wetting

5. Cold connection

6. Rosin Connection

7. Dewetting

8. Excess Solder

9. Less Solder

10. Solder Balls

11. Bridging

12. Solder Webbing/ Splashes

13. Disturbed Solder

14. Fractured Solder

15. Solder Projection