Digital oscilloscopes

An oscilloscope is an electronic instrument that is used to represent the voltage of an electronic device. It signifies one or more electric potential differences in a clear two-dimensional graph, with the horizontal axis representing time and the vertical axis showing voltage. It is used to diagnose the working condition of any electric equipment.
There are basically two kinds of oscilloscopes: analog and digital. Digital oscilloscopes use analog-to-digital converter for converting the measured voltage into digital data. The digital oscilloscope collects waveforms in the form of samples, which is then displayed on the screen when it has accumulated enough samples. Digital oscilloscopes have higher data processing capabilities.
Digital oscilloscopes are further categorized into: digital storage oscilloscopes, digital phosphor oscilloscopes and sampling oscilloscopes. A Digital storage oscilloscope is just a conventional digital oscilloscope. It displays on a raster-type screen instead of luminous phosphor. The waveform information in a digital oscilloscope can be stored, archived, analyzed and printed by the oscilloscope or by a computer attached to it. One thing that differentiates digital oscilloscopes from analog ones is that, there is permanent signal storage and extensive waveform processing. Digital storage oscilloscopes are perfect for applications that involve single-shot, high-speed, multi-channel design or low-repetition-rate.
Digital phosphor oscilloscopes are an advanced version of the digital oscilloscopes. They have unmatched acquisition and display capacities. They can reconstruct a signal very accurately. They use parallel processing architecture unlike digital storage oscilloscopes that use serial processing architecture for capturing, displaying and analyzing signals. Digital phosphor oscilloscopes rasterize waveform data and copy it to the display memory without any processing bottlenecks. A digital phosphor oscilloscope is perfect for digital debugging of intermittent signals, communication mask testing, repetitive digital design and timing purposes.
A digital sampling oscilloscope is used for capturing signals for which the frequency components are much higher than the oscilloscope’s sample rate. This oscilloscope can capture very fast signals, and also attain very high bandwidth and high-speed timing for repetitive signals. However, a digital sampling oscilloscope’s has a limited dynamic range to around 1Volt (peak-to-peak). Even the safe input voltage is very limited at 3 V as compared to 500 V for other oscilloscopes.
Agilent, B+K Precision, EZ Digital, Extech Instruments Corp., Fluke, Instek, International Tools & Technologies, Inc., Iwatsu, Kenwood TMI Corp., LeCroy, Morrow Wave, Tektronix and Yokogawa are some of the popular digital oscilloscope manufacturers. Information about digital oscilloscopes, along with their prices and product facts can be sourced from the internet. There are hundreds of websites that give information about oscilloscopes.

Understanding Transistor Cross Reference

All electronic repairers should know how to read the transistor cross reference equivalent book if they want to succeed in electronic repairs. The data sheet is very important for every engineers and technicians because it can help them to find the nearest replacement for the components that they are searching such as the transistor, scr, mosfet, ic, diode and other components.
The famous transistor cross reference book is the Philip ECG semiconductor master replacement guide. In the content you can find all kind of electronic components specification and ic schematic too. It is one of the must ‘have’ semiconductor guide for those who love electronic troubleshooting. The internal diagram or layout of ic is clearly drawn and the transistor parameters were also listed in this book. The price of this guide is not expensive and as an electronic repairer you should buy one. Just imagine without this book, you will be facing difficulty finding the right component for substitution.
In this book, many types of transistor data and specification were listed such as the bipolar transistor, silicon controlled rectifier, fet field effect transistor (Mosfet), junction field effect transistor (jfet), signal transistors, high voltage transistor such as the horizontal output transistor (HOT), silicon power transistor, surface mounted transistor, digital transistor and many other types. Although you can find a substitution part number from the normal transistor data guide book, the ECG philips master replacement book is more informative. The normal transistor replacement book only provide the voltage (v), current (amp) and wattage (w) rating for HOT but the ECG master equivelent guide show beyond than that such as the frequency , current gain (hfe) and the outlook too . Other than HOT, the normal transistor data book gives a superb or quite accurate comparison part number for you to refer.
There is one secret that I want to share to you about transistor crossreference equivalent. If you are searching substitution part number for a signal transistor, a higher voltage, ampere, and wattage will be enough but not in the case if you want to find a substitution part number for horizontal output transistor (HOT). Higher voltage, ampere and wattage will not always work because there is few more parameter that you need to take into consideration. You may ask why the transistor blow even if it has a higher voltage, higher current and higher wattage compare to the original one.
The other parameter that you need to see is the switching time which we call it the storage and fall time. Different HOT have different spec, if you really want to find a substitution for HOT, make sure you check out the storage and fall time parameter besides the higher voltage, current and wattage rating. Searching the internet for the components specification is easy-just type in the component part number follow by datasheet, data sheet, specification, spec, data, equivalent, part number, identification, marking, pinout, types, codes and cross reference. Usually the manufacturer’s website will appear and follows by other electronic supplier website. Click on the websites that you think is relevant to your search and hope you will get what you are searching.
As for the above secret, actually I have tested on quite a numbers of Monitor with the storage and fall time slightly out from the original parameter. After the replacement, the Monitor works fine but only for a very short period before it gets very hot. If I continue to let the Monitor run, I believe the HOT will blow! When I replaced the HOT with another equivalent part number that have the specification about the same as the original one, (especially the storage and fall time), the Monitor run perfectly well. My rule of thumb is, always get the exact part number first before using other number that you found from transistor cross reference book.

Programming logic control

This article provides a brief introduction into documenting software programs for Programmable Logic Controllers (PLC). Its aim is to provide clear guidance in the program documentation for PLC's.
This article is based on the Ladder Logic format of PLC Programming, but many of the points also related to Instruction List (IL) and Function Block Diagram (FBD).
PLC Programs should be written and documented so that they can be easily maintained and modified by others than those who originally wrote the program. All PLC Programming Editors have increased documentation capabilities including Siemens, Modicon, Allen Bradley and Mitsubishi.
Documenting PLC SoftwareEarly Programmable Logic Controllers had little or no capacity for the documentation of programs. For technicians to understand the logic the program had to be followed from inputs to outputs. This made fault finding or modifications to programs difficult.
As PLC's have developed the programming packages have also improved, allowing for the software to be clearly annotated.
The programming tools available for most PLC's allow for the following documentation.
Rung TitleRung CommentsSymbols and Symbol Comments.This article provides a practical guide to using these documentation techniques.
Symbols and Symbol CommentsThe purpose of symbolic addressing is to allow the PLC programmer to write the software using meaningful symbols rather than having to remember addresses.
General rules for Input and Output symbols should be to use the tags from Process and Instrumentation Diagrams (P&ID) or electrical drawing references. Where these are not available use of a simple description should be used.
For the above the following could be used.
Symbol Address DescriptionVAC01_STPB I 0.0 Vacuum Pump Start PushbuttonVAC01_SPPB I 0.1 Vacuum Pump Stop PushbuttonVAC01 Q 0.0 Vacuum Pump RunVAC01_TRAL M 1.1 Vacuum Pump Trip Alarm (Latched)VAC01_AL M 1.1 Vacuum Pump Alarm Latch (Failed to Start/Stop)
Although many program editors can allow for more characters within the symbols it is recommended to keep the symbol short and use the comments to provide further details. Our recommendation is to build the symbols from the blocks of two characters to represent the the meaning and to keep the length less than 10.
The numbers tell a tale of programmable logic controller ( PLCs ) firm entrenchment in control applications. For instance, hardware sales figures for 2001 show $80 million spent for open control (PCbased control), with $1.1 billion being spent on programmable logic controller ( PLCs ) solutions. Even as the trend is for both figures to grow by 2004, programmable logic controllers ( PLCs ) still have a sizable advantage over PCs.
Engineers these days are calling for networking capabilities. A programmable logic controllers ( PLCs ) are now low-cost dedicated controllers. They offer more processing power and have added networking capabilities with other programmable logic controllers ( PLCs ) through serial connections. A micro programmable logic controller ( PLCs ) has an Ethernet connection with optional DeviceNet or Profibus modules. So the total system is not just a stand-alone controller, but one that can network to bigger programmable logic controllers ( PLCs ). Also, increased processing speeds allow for any given programmable logic controller ( PLCs ) to do more. Because of these changes, the programmable logic controller ( PLCs ) remains a viable control option.
One trend is towards a so-called hybrid programmable logic controller ( PLCs ). These more common hybrid applications are challenging the capabilities of each control approach. Their number is growing because fewer applications are pure discrete or pure process installations. One example is a programmable logic controller ( PLCs ) on a board with sequence logic-controller functions. It plugs into a PC ISA slot and has the same programming and instruction set as a stand-alone programmable logic controller ( PLCs ). So if you already have a PC on the factory floor, you don't need to buy a programmable logic controller ( PLCs ) in a box, just the board that plugs into the PC. It has a separate power supply so that if the PC crashes, the programmable logic controller ( PLCs ) keeps running. The board also has its own I/O connectors.
Another type of programmable logic controller ( PLCs ) is an industrially hardened gateway device. It comes with a number of ports and can be loaded with a soft programmable logic controller ( PLCs ). It has Ethernet, DeviceNet, and serial communications and serves as a bridge between protocols on the factory floor between legacy systems and current systems. For instance, data from serial devices such as bar code scanners can be connected to the gateway and through the soft programmable logic controller ( PLCs ) program.
After more than a decade of articles touting the benefits of PC-based control over a programmable logic controller and predictions of the PLC's demise, this much is clear: both PCs and programmable logic controllers ( PLCs ) have their place in contemporary control systems. In many cases, they will work as a team.
In lower-end process industries such as food plants where the programmable logic controller ( PLCs ) is strongly entrenched, there is little interest in switching to PC-based control. The reason is the programmable logic controller's ( PLCs ) suitability. Sequential logic control provided by a programmable logic controller ( PLCs ) is best suited for round-the-clock operations common in those industries. In particular, a programmable logic controller ( PLCs ) can offer repeatable, reliable control conducive to high-speed, repetitive processes. Dedicated performance and a high level of security are also benefits of a programmable logic controller (PLCs ). The packaging side of a food plant lends itself well to sequential logic control which makes a programmable logic controller ( PLCs ) the best choice for conveying and sorting applications.
Five years ago, the prediction was that PCs were going to take traditional programmable logic controller ( PLCs ) applications by storm. The reason they didn't is that the programmable logic controller ( PLCs ) has continued to be a good, low-cost control option. For instance, a programmable logic controller ( PLCs ) with highspeed counter inputs, loop controls, analog points, and basic math calculations are available in the $200 to $400 range with 100 or more I/O and with options for expansion. On the other hand, even buying an inexpensive PC requires loading software, setting it up, and making sure it's robust enough to not crash.
However, PC-based control has its merits. Specifically, it has greater number-crunching capability, more communication options, and is geared more toward data logging and trending, plant monitoring, report generation, and documentation. The key reasons to switch to PC-based control include networking the control system to higher-level applications such as ERP, handling complex mathematical applications such as vision inspection systems, and connecting to bar-code scanners, in-motion weigh scales, and other devices. In short, most users believe that when data must be transferred from the controller into a database for analysis, the transfer goes more smoothly when the data is already on a PC-based system.

Testing diode

Testing diodes is different from testing a resistor because you need a skill to do it. If you do not know or wrongly test a diode you will be unable to repair the equipment. A bad diode you think it is good. This will definitely waste your precious time.
A rectifier diode can fail in one of the four ways. It can become:
-Open-Shorted-Leaky-Breakdown when in full operating voltage
An analog multimeter or digital multimeter can be used to check for all the first three conditions except the last one where the diode breakdown in full operating voltage. From my of experienced in the electronic repairing line, i found that checking diode using analog multimeter is more accurate than using a digital multimeter. I could explain to you why i preferred analog meter. I do not know about you because i really came across quite a number of diodes where it checked ok using digital multimeter but failed when test with analog meter.
The first step on how to test a diode is to remove one of the diode lead. You can't always be certain if a diode is good or bad if you perform in-circuit test, because of back circuits through other components. To be absolutely sure, you will need to lift, or disconnect, one diode lead from the circuit to avoid back circuits. Unless you are very sure about the board you are checking. Sometimes i do found bad diodes when checking it on board. Your experienced will tell you when to check a diode on-board or off-board. If you are new to electronic repair, i highly recommend that you check a diode with a lead removed from the board.
I will set my analog meter to x1 ohms to check for current diode leakage reverse and forward testing. Connecting the black probe of your meter to the cathode and red probe to the anode, the diode is reverse biased and should look like an open reading. Connecting the red probe of your meter to the cathode and black probe to the anode, the diode is forward biased and the meter should read some value of resistance. If you have two readings then most probably the diode is shorted or leaky and you should replace it. If you don't get any reading either forward or reverse bias, the diode is considered open.
The real problem when checking a diode using the diode test function of a digital meter is that an open or leaky diode, the meter sometimes reads ok(0.6). This is due to digital meter diode test output voltage (which you can measure the output test probe using another meter) is around 500mv to 2v. An analog meter set to x1 ohms have output about 3V(remember the two 1.5V battery you installed in the meter!). The 3V voltage is enough to show you the accurate reading of a diode when under test.
Even if you have a good reading at x1 ohms doesn't mean that the diode is good . You now have to set your meter to x10K to test the diode again. The output voltage of x10k ohms is about 12V(remember the 9v battery in your meter-1.5v+1.5v+9v=12v). Again the diode under test should show only one reading. This is exception to Schottky diode where it have two readings but not shorted reading. If the meter showed one reading then the diode under test is good. If it has two readings then most probably the diode is either shorted or leaky. The digital meter can't test it because the output from the meter is only 500mv to 2V.
If a diode breakdown when under full operating voltage, there is no way to testing diode (unless you have a very expensive diode checker which specially designed to locate this type of problem).Substituting with a known good diode is often the only way to prove that an intermittent diode is causing a particular problem. Sometimes an intermittent diode could be locate using a coolant spray.
Caution: Be certain that power is removed from any circuit before performing any of the following diode checks, otherwise meter or circuit damage could result.
Conclusion-In order to correctly test diode function you need to set the analog meter to x1 ohms and x10K ohms range.

Understanding resistor color code is very important if you want to calculate the resistor values of a particular resistor. Each resistor color band represents a number where you could refer to code below to help you to find the standard resistor value. The resistor coding act as a resistor calculator and with examples given, it would not take you a very long time to understand it.
0=black, 1=brown, 2=red, 3=orange, 4=yellow, 5=green, 6=blue, 7=violet, 8=grey, 9=white, gold=5% and silver=10%
Red, red, orange, gold = 22 multiply by 1 (orange equal to three zero), so you get 22 multiply by 1000 =22000 ohms or 22 kilo ohms with tolerance of +/-5% (gold).
Blue, grey, brown, gold = 68 multiply by 1 (brown equal to one zero), so you get 68 multiply by 10 = 680 ohms with tolerance of +/- 5 %.
Brown, black, yellow gold = 10 multiply by 1 (yellow equal to four zero), so you get 10 multiply by 10000 =100000 ohms or 100 kilo ohms with tolerance of +/-5%.
Yellow, violet, gold, gold = 47 multiply by 0.1 (gold at third band), so you get 4.7 ohms with the tolerance of +/-5%
Orange, orange, silver, gold =33 multiply by 0.01 (silver at third band), so you get 0.33 ohms with tolerance of +/-5%.
In electronic repair, most of the time i came across five band resistor color code. The purpose of using the five color band resistor in a circuit is that it provides a more accurate value compare to the four color band. For example in order to get the value of 22.6kohm, with four colors band resistor you will not be able to find it. The most you can get is 22k (red, red, orange and gold).
If with the five color band you will be able to calculate it (red, red, blue, red, brown) the last color which is brown represent 1% tolerance. If you open up an analog multimeter you will understand whatIi mean. Most of the resistor circuits inside the multimeter are using five color bands. Why? Because the reading that you get whenever you measure current, voltage or ohm, the panel will show the nearest value. For instance, if you measure a 9v battery the needle will point to may be 8.9v, 9v, or 9.1 volt. If that particular multimeter was designed using four colors band resistors the result that it gets may be 8.5v, 9.5v or even 10 volt. In other words the use of five colour band resistor is to make a circuit more precise and output the desire result as what the engineers want it to be.
If you come across any wire wound resistor, there are numbers printed on the resistor and each coding represents a resistor value. Below are the formulas that you can use to find out the exact resistor values:R82 is .82 ohm, 15R2 is 15.2 ohm, 100R is 100 ohm, 10K is 10 kilo ohm, 2K7 is 2.7 kilo ohm, and 2M2 is 2.2 mega ohms. Hope you find this resistor color code article useful and be able to calculate resistor value in the shortest time.

All about electronic

Electronic components form parts of electronic circuitry, and are used or manufactured in the field of electronics, which is the study of electrical devices used for controlling electrically charged particles or the flow of electrons to execute any electrical operation. Some of the most common electronic components are as follows:
Resistor: A resistor resists electric current, and the resistance is measured in ohms. Colors on the body of the resistor are a code for the value. Different colors represent the numbers from 0 to 9. In a variable resistor, resistance can be varied by moving a knob or slider. A variable resistor is used to control volume in many devices.
Capacitor: This is measured in farads. A capacitor is used for storing electrical charges that can be released upon demand. Capacitors can be of different types – electrolyte and ceramic disc are two of them.
Diode: A semiconductor device, diodes allow current to flow in one direction only.
Small, cheap and lasting, light emitting diodes (LEDs) are special diodes that give out light and allow current to flow in one direction.
NPN bipolar transistor: Used for current control, they can amplify currents with a small amount of heat dissipation and very little spatial waste.
PNP bipolar transistor: Its functions are the same as NPN, but construction is slightly
different.
Crystal: When a voltage is applied, crystals can accurately vibrate a specific frequency.
Integrated circuit: Having circuits etched into it, an integrated circuit is a semiconductor wafer that can hold capacitors, resistors, transistors, etc. in a large quantity. By allowing the chips to have millions of transistors, integrated circuits are capable of saving space.
Triac: A dual silicon controlled rectifier (SCR), triac is used to control alternating current (AC). Mostly used in dimmers and touch lamps, it controls the amount of electricity reaching an appliance.
Tapped secondary transformer: Used for transforming voltages, a plug-in transformer, the wall type, changes 120 volts AC into about 12 volts DC for small appliance needs. In a tapped secondary transformer, the secondary winding of the transformer is connected to a wire so that it can be used for multiple voltages, or more current.
Speaker: A speaker converts electrical energy into sound energy.