Monday, August 06, 2012

Front End Security for SMPS

Now we have smps in most everything. AC Adapters and CFL lamps and many Home Consumer Electronics. The Failures of these units are on the rise. The Cooper transformers are out, but the SMPS reliability is falling.

Designing and manufacturing a SMPS facing a 230V input constantly, is not easy. You cannot Mutz your way in this, in a cost-cutting spree of this Vital Organ, just to have a competitive advantage of 'a lower cost product' (read cheap).

Now 230 V AC 50 Hz is not what you think it has, it has EMI-RFI, Inductive Kickback Spikes from the neighborhood, resonating and ringing with the RLC network that your home wiring forms. Lightning and Atmospheric Static that may strike at the weakest part on the SMPS. Wrong wiring, 3 phase mess ups. short circuits, falling tree branches, thunderstorm. Your SMPS is facing the Real Harsh Cruel world and the best part, they left off the Security Department to keep costs low. The critters in the box get zapped for no fault of theirs.

Front End Security for SMPS

There is one difficult way out of this, we move to a 24V DC standard within the house, it is safe and the Box outside the house faces all the Electrical Environment Variables and Unpredictability. This box that charges the battery and steps down the mains voltage can be protected well. Protection on this one unit, protects all the equipment in the Home or office. This is the Civilized way electricity should be used in Homes and Offices. Easy to integrate with Alternative energy. Factories can have all the High Voltage they want.

When a good technical collaborator is involved, quality is given due respect, the products are affordable yet robust. Some firms cut off vital circuitry (these happen in mechanical, electrical and chemical field too) to keep the product cost low. These products will work well in a Mains conditioned environment which is only affordable in some companies and never at homes.

The Security system consists of something that a Surge Protector from Belkin has. Let us see the traditional way, We need Gas Discharge Tube Lightning Arrestors. Then Varistors, Thermistors, X and Y caps and the Common Mode Choke Coils. A high voltage and high current fast acting fuse or trip circuit. Overrating of Mosfet and caps that face the high voltages. Using HV Back-to-Back zeners with fuses. Snubber Plastic HV self healing caps and Fast Switching diodes to absorb the inductive spikes.

Do it within the budget you have. SMPS should withstand 1.2KV microsecond pulses. 600V millisecond pulses and 400V for a few seconds. 300V AC for many minutes. Else let us go 24V Standard.

Other Protection devices your house or lab may needs to have. CVT - Constant Voltage Transformer, 1:1 Isolation Transformer, Servo Motorized Auto-transformer Stabilizer, Earth Leakage Circuit Breaker, HV-Relay Trip Circuit, Overload Current Relay Trip Circuit, MCB, Switched Triac or Relay, Copper Transformer Stabilizer with Layer or Layer Primary Insulation to protect against high voltage. This transformer should have earth shield, guarded terminals, primary windings should not slip layers, Vacuum Impregnated. 

May the Earth be good to you ! - Means - the earthing in your Home of Office should be excellent and do not compromise on Wiring Insulation and Switchgear. Let the wires outside have concrete gutters which are closed so that water or rodents do not get to the cables.

Read more at my Power Electronics Section

Tuesday, February 21, 2012

Analog Interface for PC Ports

Here are examples of an analog Input and Output interface for Printer Port. There are two visual basic demo programs with source to test out idea.

Analog Interface for PC Ports
USB and wireless interface to PC may be more in vogue, but a higher speed is possible in printer-port. For analog and digital fast data acquisition, PC cards to full Access to PC bus are the best choice.

Analog Interface for PC Ports

The Sensors and Actuators interfaced with a computer form a basic automation system or even a robot. So learning to interface Sensors (input devices like a thermocouple or pH sensor) and Actuators (output devices like a motor or heater) with a PC is the best way to start. It is by studying examples and experimenting cautiously can one learn the science, book reading alone will never help.

See the Hardware Book connector details, cables, adapters, etc. The RS232-Serial Port, The Parallel- Centronics port, The USB-firefire port are good to start with. Then you can interface by LAN or Wireless- LAN or TCP/IP-Internet to make Robots or Automation extend to multiple places and computers. The possibilities are endless, imagination is the limit for students. But entrepreneurs need to be practical and only make equipment that have a utility and sensible market scope.

The circuits and code have some errors, The documentation is not complete.
DVM = digital volt meter MVS = milli volt source

Friday, February 10, 2012

Temperature Control - Part 2

A Two Point Process Controller or Temperature Controller would look like this. When a High-Low Alarm Protection for uC based Controller was needed the same was modified and used.

Sometimes uC based instruments just forget and that can be costly, the watchdog timer has solved this problem. In Industrial Process Control we cannot take any chances, so a two tier or even three tier protection is required, especially so if the Job or Raw material being processed is expensive. So Real Time Analog Trip + uC Controller is safe. Then you can still have Electro Mechanical Devices for Extra protection against Fire or Meltdown.

Two Setpoint Temperature Controller

Temperature is the most common process parameter, Pressure seems to be next. Flow, Level, RPM, Distance and many more follow.

When a physical parameter let us say distance is measured, we first need a sensor that converts it into electrical values, digital or analog. The sensor used for length is a Linear encoder and it creates the electrical information for the DRO to Display.

Now many sensors like a strain gauge produce very low and weak signals and some are non-linear. So the signals undergo Amplifying, Temperature compensation and Linearizing together called Signal Conditioning. This stage outputs some standard values like 4-20mA, 0-10 V, 1-5V, or even directly digital or wireless in the new technologies. Even when a digital interfacing standard is used, amplification and some signal conditioning is required at sensor end. Compensation and Linearizing can be better done with a uC using Math or Look up Tables.

When you have many different parameters then it is better to use process controllers with a 4-20mA input standard. Then the inventory of controllers can be reused for any process.

It is always better to use sensor-end transmitters to get 4-20mA to your Controller, Recorder or SCADA System.Weak signals are corrupted by noise and dont travel long wire distance. Junction EMF at joints and terminal blocks add to errors. These are overcome by the 4-20mA signal that has the juice and punch to transmit the data over the shop floor to the control panel rooms.

Read more here Temperature Measurement and Control

Monday, January 30, 2012

Temperature Control in Automation

Temperature Controller 48-96 - A 1/8 DIN Indicating Temperature Controller. This is a Analog Controller built around ICL7107.

Temperature Measurement and Control

48 96 Temperature Controller

This is a 48-96 DIN Temperature Controller, it is mains operated, it is in a Industrial Plastic Housing. It is not meant for very harsh environments. Suitable for Control Panels in Control Rooms. It has a accuracy and linearity of 0.5%. It had options of on-off or time proportional control.

Complete designs and PCB of a Generic Analog Controller

Main Cards having Power Supply and Digital Display

Signal Conditioning and Control Modules on BergStick/soldering.