delabs Circuits

Monday, August 07, 2006

Insulation Resistance Theory

Insulation resistance is a very complex parameter, but it is very important to study it in the field of electrical & electronic engineering. The I.R. value, of a specimen changes with time on continuous application of D.C.voltage, the IR value changes with change in magnitude of the applied DC voltage and IR value also varies with Temperature, Humidity and contamination. When measurement is made, the IR value slightly increases after each measurement cycle. This is due to residual polarization of the previous application of voltage due to all the above factors, IR measurement becomes both difficult and complicated. The DRT 101 overcomes most of the conventional problems and makes Insulation resistance analysis more scientific & practical.

The problem of residual polarization can be overcome by :
  1. The terminals of the insulation shorted for a few minutes.
  2. The terminals are reversed after each measurement.
The DRT1C11 shorts the specimen terminals automatically when it does not apply voltage. But most accurate results are obtained only on, the 1st measurement on a specimen or by giving a gap of 30 mts for depolarization between each measurement.

When a steady DC voltage is applied to an insulation, the observed behavior is a analogous to that of changing a leaky capacitance through a series high resistance. The resultant current comprises of these components.
  1. A charging current due to the natural capacitance. This is large in the beginning and becomes negligible in a few seconds.
  2. The absorption current flaws in the body of the dielectric and decays with time. The time may run to many minutes, this absorption current gives rise to polarization residue effect.
  3. The actual conduction current through the insulation. This is constant with time. But can vary with voltage & temperature.
  4. The surface leakage current depends much on Humidity contamination.
Insulation may fail due to the following reasons:
  1. Mechanical vibrations may rupture insulation.
  2. Temperature decreases thermal strength.
  3. Dust & moisture cause contamination & decay.
  4. Corrosive material & electrochemical reactions.
Mode of insulation failure :
  1. Intrinsic breakdown.
  2. Thermal effects.
  3. Ionization.
Methods of measuring high resistance and IR :
  1. High voltage bridge.
  2. Leakage current measurement method.
  3. Loss of charge method.

Pages 1, 2, 3 of DRT101 Insulation Tester and Tera Ohm Meter Operating Manual, A product that i used to make-n-sell. - delabs

Saturday, August 05, 2006

High Resistance Materials Tables


20 C OHM -M
min max
Benzene 1011 1012
Transformer oil 1010 1013
Gasoline 1010 1013
Castor oil 108 1010
Acetone 104 105
Ethanol 104 105
Distilled water 103 104

Glass At High Temperature

200 C OHM -M
Sodium Pyrex 2 * 106
Potassium Pyrex 8 * 109
Lead glass 2 * 1011

Effect Of Contamination On Surface Resistivity

Window glass 2 * 108 1012
Fused quartz 2 * 108 1013

Relation Of Resistivity With RH % And Temp

MATERIAL 70% RH 20 deg C 0% RH 100 deg C 0% RH 20 deg C
Marble 106 - 108 1010 - 1012 1012 - 1014
Wood 106 - 107 1010 - 1012 1011 - 1013
Vulcanized fibers fibers 106 - 109 108 - 109 1011 - 1012


Polyethylene 1017
Poly propylene 1017
PVC 1018
Polyurethane 1015
Asbestos fiber + phenol 108
Mica + phenol 1012
Glass-fiber + polyester 1012
Glass-fiber + epoxy 1014

Thursday, March 30, 2006

Resistors and How they Work

Resistors start from Wires to Wirewound Types. Carbon Film Resistors are most Common, Metal Film Resistors are more stable and accurate. We have now SMD types with lower power some are Laser Trimmed Types for accurate values. Resistors Arrays are used in Digital Circuits.

Types of Resistors - Color code and Other Resources

1/4 W Resistors have a Voltage rating of around 200-250V. Even when using a High value like 1 Meg use two in series when it is across Mains 230 V AC. 470K + 470K - you get around a Meg at 500V Rating.

1/4W Metal Resistors Riedon MFR Resistor Networks Audio Gold LVC Ser LVC-1
Futurlec Riedon Caddock Ohmite Ohmite
1/4W Metal Film Resistors.
High stability
Solid construction
1% tolerance
1R to 10M
1 Ohm to 10 Meg Ohm
Tolerance to ± 0.05%
Low Temp. Coeff.
TC ± 3ppm/°C
Very Low Inductance
Matched Sets Available
39 standard models
Type 1776
precision resistor networks
Absolute Tolerance
Absolute T-Coeff
3 watt to 50 watts
Non-inductive available
Reduces signal distortion
Minimizes thermal EMI
Standard Sizes
Terminal Barrier Resists Ag Migration
-55°C- +125°C
Auto Insertion
1% MFR
tight tolerances
Highly stable
low noise
low temp-coeff
demanding applications
minimum tolerances
long-term stability
3, 4, and 5 - decade voltage dividers
10:1 - 10,000:1
1,200 volts continuous
overvoltage to 2KV
wire wound
ceramic core
high-end loudspeaker
amplifier applications
low value
chip resistors
current sense applications
low profile, cost

Coils and Transformers for SMPS

Coil Winding Specialist Coil Winding Specialist Coil Winding Specialist Coilcraft, Inc Coilcraft, Inc
Toroid Inductors Axial-Radial Coils EE Core Transformers Pot Core Trx Drum Core Coil
High Q
Low Cost
Difficult to Wind
Easy To Mount
Very Low Cost
Low Q
RF Radiation
Easy to Wind
High Power and Q
More Pins, Robust
Air Gap Adjust
Split Bobbin Too
High Q
Low Profile
Small Footprint
Easy Mount

Application Notes of CWS Design Tools Coilcraft mobius winding techniques
Switch Mode PS Transformers Producing wound components Ferrite Inductors
educational encyclopedia inductors Power Transformer Inductor Switch Mode Power Supplies
Inductance and Inductors Inductors SMPS Basics Buck Converter
Ian Purdie "Toroids" Axial Inductors ECM Cores of Magnetics

Mains Transformers Types

These are Transformers Made by Hammond Manufacturing
Classic Transformer Terminals Transformer PCB Transformer Toroidal Transformer
Split bobbin assures product safety.

Easy Cabinet or Panel mount.

Wires for connection-termination.

Mechanically Sturdy, use 'lock nuts'.
Easy replace on service.

Panel-Cabinet Mount.

Clamp Serves as Shield.

Split Bobbin Insulation.
Mount on PCB and Solder.

More Reliability, no-wires.

Winding slip not possible.

Make Modular supply card.
High Efficiency.

Low Heat inside box.

Low Profile and space.

Long Life and low EMI.


Basic Electronics
Basics of Electronics
Product Production
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Testing Points
Learning Electronics
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Production Notes
Prototype Fabrication
Electrical Circuits

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

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

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
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Electronics Tutors

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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

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