Wednesday, September 10, 2014

Electronics Work Culture and Discipline

Systematic and Meticulous work has its own Rewards. An Engineers Notebook or a Hobby Experiments Log Book can go a long way in making a Cauliflower out of every Cabbage. (The credits of the Vegetable Analogy goes to Mark Twain)

1. Keep Work Place Clean.

Clean Tables and shelves every day before closing office, Put Cut leads and Solder shots in a separate cup to be accumulated and disposed later as these are toxic. In this cup other irritants like staple pins can be added and these can be clubbed in a month and disposed off as one metallic bulk for recycling. Never bring coffee or food to work area, Keep a waste paper basket on your side.

2. Work carefully to avoid injury

When cutting leads hold the lead in the hand and cut or it will fly all over the place. A piece like that may land on another equipment and cause shorts or it may go right into your eyes and cause blindness. Lead and Iso propyl alcohol and other Chemicals may be dangerous for health if handled carelessly. Do not use fingers, and teeth as tools it is bound to cause a injury to repent a lifetime. Be extra careful with 230V AC and more so with 440V 1 tr 2mA thru your heart and a weak streak of luck may be the last experience you ever had. Do not press your Luck too hard.

Electronics Work Culture and Discipline

3. Protect Desk or table surface.

If you are cutting something let it not leave marks on table, even adhesive stains should not deface table, use a asbestos, Bakelite, fiberglass, hardboard surface which can be disposed once in a way. Before working put two layers of news paper on the table this prevents table from getting spoilt while soldering and newspapers being hygroscopic (water absorbent) they provide a natural antistatic surface to protect CMOS Ics and are nonconductors for any Live PCB kept on the paper.

4. Use tools and equipment's in a gentle manner.

When you use weller Iron use it as a heat transfer tool never use it for prying or crimping leads or just pressing use pliers or other tools for that.

5. Document what you do and vice versa.

Have a register in which you can make records of what you did to solve a problem or what you learnt while making an equipment this information is valuable for the company to develop production methods and also useful to your team to solve a similar problem. Share abilities and skills with fellow employees but don't share your company's technology and database with any other company. When you leave a company use only the abilities and skills in that broad area to evolve as a professional.

delabs notes - 80s and 90s

Tuesday, September 09, 2014

Fluid or Water Level Indicator with Reed Relays

This is a way by which you can monitor the level of fluids like water in a tank. Based on data from the sensor you can control things like solenoids or motors as required or even turn on a buzzer, hooter or annunciator in a control panel.

Fluid or Water Level Indicator with Reed Relays
Description.

Look at the picture on the right, the float can be a Styrofoam type with a couple of ceramic magnets stuck inside. The float must move freely up and down a long plastic pipe of around 10 mm dia. If the fluid is not water but a solvent then design a non-soluble float or coat the float you made with something like an epoxy resin.
Then you need to assemble a small circuit within the long plastic pipe. Many reed relays with a chain of resistors in series has to be inserted in the pipe. The resistor and the glass reed relays should be in different levels of the pipe where you need an alarm or indication. Seal the pipe hermetically at both ends with epoxy resin after taking out a shielded cable of just 2 wires + 1 ground shield.
When the fluid level changes, the float moves up or down with it, when the float moves over a section of pipe where the reed relay is mounted, the magnets on the float make the reed operate and the resistance of the sensor changes.

The resistance is measured and the alarm can be operated as you like. The advantage of this arrangement is the electric circuit does not come in contact with the fluid, no sparking risk.

Reed Relay. It was invented by Dr. W. B. Ellwood at Bell Labs in 1936. Contacts are in a sealed glass tube filled with inert gas like in a bulb, so they do not corrode. It is faster than regular relays and as no spring is used it has a longer mechanicalreed relay life. The two contacts are ferromagnetic blades plated with rhodium. When you take a magnet close by, the contacts touch each other. You can also put the reed in a coil, then when you energize the coil the reed operates. Used in telecommunication.OKI is one manufacturer of this type of component.

Design and Caution.

When you drive inductive loads you have to use RC snubbers, freewheeling diodes, varistors or zeners. when you drive lamps the cold current is high so use thermistors. The Reed relay is best used in telecom and instrumentation and avoided in power electronics. It can handle high RF frequency as the path of current is straight and footprint small.

Here is a Circuit to Build and Learn this Concepts -

Fluid or Water Level with Reed Relays

"When you use the DMM or digital multimeter, try not to use it for high voltages and currents, use Solderman Talks 1702external shunts and attenuators instead. If you try to measure 230V AC in the Ohms mode or in the Current mode with the probe in the current socket then you will see fumes in your DMM and a hole in your pocket !!" 

- Solderman Talks 1702

Saturday, September 06, 2014

Thermocouples and RTD Tables

The easiest way to measure temperature is with a glass diode like 1N4148 or a metal Transistor like 2N2222. These have a small temperature range, probably -5 to +120 is possible, but non-linear. A copper coil or any metal wire or even a wirewound resistor can work as temperature sensor but the thermal inertia makes it sluggish. IC semiconductor based sensors like LM335 and AD590 are easy to work with and pretty accurate. In industrial environment many types of Thermocouples, Pt-100 RTD and Optical Infra-Red Temperature measurements are used.

Input Levels for Thermocouples and RTD Pt-100. And the ways it has to be used. Thermocouples are selected on the basis on how they are mounted or fixed, the environment, the temperature range that is measured and finally the price you can afford for a particular application. Sometimes mechanical wear or chemical environments may eat away the sensors, so a cost-effective solution has to be evolved.

One customer wanted a special Pt-PtRh very high temperature sensor for molten aluminum. It was very difficult and costly to even arrive at a solution. So a non-contact infra-red sensor may save lot of time-money and even reduce risk of injury.

Thermocouples and RTD Tables

For J, K, and T Thermocouple Read "Temperature" + Room Temperature for mV shown applied to equipment, eg....

If Room Temperature is 25 Deg C and mv applied is 10.777 for J Type STC1000 then reading should be 200 + RT = 225 deg C. The mV shown are for Reference Junction at 0 Deg C.

It would be better if you refer links below, The above table i made long ago, then a Scan with OCR later formatting. It could have errors.

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Contents

Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits
Electromechanical


Library
Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits


Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07


Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition


Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent


Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525


Embedded
Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Components
Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

History
Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments


Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

Analog
School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors

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