Technical-Reference (Page 5)

Technology Resource – Silicon Sam

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Series and Parallel Transformers

Series and Parallel Connections in transformers. Observe the Dot-Polarity. When windings are in parallel the current capacity doubles. When windings are in series the voltage doubles. Wrong dot polarity in series connection just cancels the voltage and a small residual imbalance voltage remains. If wrong polarity connection is done in parallel, then a short circuit or overload may occur.

Basic Electrical Circuits

Series and Parallel Transformers
Center Tap Transformer

This is when you need to build a symmetrical dual supply like +12V and -12V supply for an opamp design.
This is also good for a two diode full wave rectifier. But when you make a dual supply use a bridge and the center tap is ground. If you use just two diodes then one winding may be loaded more than other. That may not be good for long term transformer life. The core may get magnetized.

Center Tap Transformer

Contactors are used to switch Mains voltage. even three phase power to Motors, Heaters and other Actuating Elements of Industrial, Home or Energy Automation. The Types below. They carry high currents and hence are mounted on Panels and Sealed Enclosures.

What is a Relay – Jim Asks

Top three images –

Smart Contactors. Timer, Thermostat. Over Current or Voltage. Trip or Limit. Three Phase Trip. High Power. Solenoid hammer.

Power Contactors. High Power. Nut-Bolt Mounting. Solenoid hammer. Special Contacts. Special Plastics. Heaters and Motors.

Din Rail Contactors. High Power. Easy Replace Rail Mount. Solenoid hammer. Heaters and Motors. Modular, Stackable. SCADA, Control Panels.

Relays and Contactors 1

Bottom Three images – Relays are much smaller, they are power switching relays and signal switching relays. They are mounted on PCBs or on cabinets/enclosures.

Then we have power relays, like the three above. They may be mounted on PCBs or Inside the Cabinets. They switch currents upto 5 Amps and voltages upto 230V. These are used in Home Automation and in Instruments. The Signal from these drive Contactors in Large Power Systems.

The PCB Versions should not be used for high currents, use for signalling contacters or driving Lamps and Hooters in Annunciation and Alarm systems.

Medium Power. Solder Terminations. Panel Mount. Solenoid hammer. Low Cost. Time Tested Design. Commercial.

Low Power DPDT. PCB Mount. Solenoid hammer. Visual Isolation. Switches Two Loads. Industrial.

Low Power. Small Footprint. Solenoid hammer. Communications. Appliance Control. Low Cost.


In image below – see top three images

Medium Power. Panel or Rail Base Mount. Solenoid hammer. Visual Isolation. Easy Replace, Plugin. Industrial.

Medium Power. PCB Mount. Solenoid hammer. Visual Isolation. Switches Two Circuits. Industrial.

Low Power SPDT. PCB Mount. Solenoid hammer. Visual Isolation. Controls Contactor. Industrial.

Relays and Contactors 2

Bottom three images are Analog or Digital Signal Relays, means very low current, Low voltage. It is used in Instrumentation, Communications and circuit multiplexing.

Micro Power. Telecommunications. Analog Signal Switch. Low Capacitance. Low Inductance. Reed Relay.

Micro Power. Analog Signal Switch. Small Footprint. Reed Relay. Instrumentation. Communications.

Micro Power. Analog Signal Switch. Small Footprint. Reed Relay. Communications. Low Ripple Pickup.

Choosing a relay–  A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.

Relay Timing –   The text covers electronic circuit to sequence and speed separate relays (like dual vacuum relays) and describes how to sequence mechanically ganged contacts like those in open frame relays.

Relay – Wikipedia  – A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts,

Wet bulb and Dry bulb Digital Humidity Meters or Hygrometers are accompanied with a chart for evaluating % RH. This chart is in PDF format below.

Table of Relative Humidity or RH 370 Kb PDF

The Sensors that could be used are Two RTD PT-100 and Two 48*96 Digital Indicators. The Wet bulb had a Moist Wick Compartment where water has to be refilled periodically.

Here are some Traditional Hygrometers. Even today these are used and work very well. Humidity and Temperature control is also important for HVAC – Heating, ventilation and air conditioning (HVAC).

Relative Humidity Table for Hygrometer

When Weaving Textiles, Humidifiers or Atomizers are used to maintain the Humidity of the Work Area where the Looms are running. A Horse Hair Hygrometer is used to Manually Monitor and Regulate the Humidity. In Offices where the Air Conditioning needs a Humidity regulation the method used to Determine Humidity is by using a Wet and Dry Bulb Hygrometer or a Sling Psychrometer. Human and Animal Health is also sensitive to these parameters.

Related Resources –

Here are some Test and measurement notes. These ideas come from practical experience. But the jots are not in any order but are quite important.

Instrumentation and Automation

Scope Notes

  • If the waveform on the scope droops then you may need to use a 10X attenuating probe or mode. this attenuator is at the tip of the probe hence better measurement possible, also very high frequency signals may be best transmitted over a 50 ohm impedance matched line to the Oscilloscope.
  • Karl Ferdinand Braun – In 1897 he built the first cathode-ray tube…oscilloscope. CRT technology is to this day used by most television sets and computer monitors. The CRT is still called the “Braun tube”.
  • Do not use an oscilloscope to measure 230V directly, use a transformer, differential probe or attenuator.
  • An oscilloscope 1M probe or a DMM 10M impedance can load circuits with nano-pico amps of bias.

DMM Notes

  • Test a NPN transistor, DMM in 200K range. emitter negative probe, collector positive probe, it should show open. while still holding that way press wet finger on base and collector, it may show some reading, then it is ok. for PNP swap probes polarity and do the same thing. the wet finger when pressed applies a base current in uA.
  • The most common reason of DMM failure is when a person tries to measure 230V AC with a DMM in current or ohms mode, with the probes in the wrong sockets. Use external attenuators and shunts.
  • A DMM in diode mode or resistance mode can be used to test IR diodes, take it under 100W lamp and measure, cover the IR diode and measure you will see a response in proper polarity.
  • If you put the DMM in 2V mode and measure the voltage across a ordinary LED near a 40W lamp you will see around 200mV. Turn off 40W lamp the mV will fall near 0. Even metal-can transistors with their top ground away will become photo sensors.
  • When you measure low voltages or high resistance like 1M with a DMM your body must not be in contact with the probe tips. Body resistance is low in comparison so error in reading or loading of mV from sensor, in sensitive and high impedance ranges.
  • Red socket and probe for positive and black socket and probe for negative
  • Is it oscillating ?…. We cannot say, it could also be DC, you need to see if a Clock is present. use a signal tracer or a DMM freq mode, or AC measurement. or build this solorb.com-elect-logprobe. When you do not have a scope you can build one for the PC.
  • Polarity and Zero Cross indicators tell you to swap the leads. Use a comparator or opamp to build it.

LM335 and LM336 –

LM335 is a temp sensor, LM335 . use it for temp for CJC. Temperature Sensors – RTDs and Thermocouples in Temperature Measurement.

LM336-2.5 is an voltage Reference. precision 2.5V shunt regulator diodes, Applied as a precision 2.5V low voltage reference for digital voltmeters, power supplies or in opamp signal conditioning.

Current Loop –

4-20 ma will drive DC drives, motors and steam valves. It is a current loop, for long distance transmission, current loop is not prone to noise and hum, EMI RFI. As it is a small power transmission no loss of data, also many equipments can be in one data loop. A single transmitter with 4-20mA out can drive a strip-chart recorder, motor, controller and SCADA input. all in a series loop. Current loop is like 4-20 mA

Opamp Notes and Types

  • TL062, LF353, TL072, fet input. 1 tera ohm input imp.
  • OP07 higher price, 1 giga ohm. 75uV offset.
  • LF353 pin to pin replacement of TL062-72 and 82.
  • LM358 works on single supply too, low price, inp imp 1 meg.
  • LM324 Quad, works of batteries well.
  • All work best with dual +/- 5 V or more. LM7805 -LM 7905.

Points to Note –

  • Analog ground (opamps), digital ground (CMOS) and power ground (relays and LED) should be separate, (linked at root)
  • Glass epoxy PCB have high insulation resistance, above 10 tera ohms, and are not hygroscopic which means they do not drink water vapor, this makes them very suitable for precision instrumentation and sensitive circuits.
  • When you measure DC levels in 16bit accuracy or more you need resistors which have temp. coeff. of 10ppm, or you may have to put the entire circuit in a stable 45 deg oven. Thermoelectric effects, EMI, RFI, pA Leakage currents, ground loops, contact resistance all can make the readings drift and unusable.
  • High impedance points of circuit like 500 kilo ohm and above can pick up AC noise and DC leakage currents. this will affect the performance of circuit, so for DC you have to put a guard ring of the signal ground around that point in PCB. For RF you have to shield with things related to iron and mu metal, for low signals even a copper shield will do.
  • Percentage and ppm: when percentage becomes like 0.001% it is difficult to manage, so we use ppm-parts per million.5% means 5 parts in 100 parts. 23 ppm means 23 parts per million parts. 0.001% – shift the dp-decimal point four places to right it is 10ppm. 0.01% is 100ppm which is the variation of value of mfr resistors on temperature change.

Learn this at my Industrial Process Control Circuits

Source for process measurement and control. Everything from thermocouples to chart recorders. Temperature, flow and level, data acquisition.

Established in 1962, Omega started as a manufacturer of thermocouples. Now it is a Technical Supported Marketplace for Industrial and Engineering; components and equipment. It is also a Engineering Service with custom product and system solutions for your Automation or Laboratory needs.

Omega Engineering

Omega Engineering – Industrial System Materials

Omega’s Technical Reference Section. Find technical articles and reference material about their products and technologies. Omega’s Temperature Handbook Technical Reference Section.

Omega Engineering – Technical Reference Section

Whether you are an Industrial Control Engineer, Equipment Manufacturer or doing Research in a Laboratory; these Catalogs and Books are a Valuable Reference, from one of the Oldest and Reliable Source of Technical Information and Products. – delabs

8/16-Channel Thermocouple/Voltage Input USB Data Acquisition Module

The OM-DAQ-USB-2401 is a portable USB 2.0 full speed thermocouple/voltage input data acquisition module that can be used with either desktop or laptop PCs.

OMEGA Engineering, Inc.
One Omega Drive P.O. Box 4047 Stamford, Connecticut 06907-0047, USA