Electronics Engineering Magazine

Monday, December 15, 2014

Closed Loop Control Systems

A Closed Loop Control System is the most important aspect of Maintenance, Regulation and Stability in any Live Process. Nature itself is self regulated in an intricate fashion, a keen observer can notice the subtle controls. In Human Created Industrial systems we have Process control as a complex science. We can start by understanding a Simple One.

Process Control Application Notes

When you fill a Bucket with water, You keep an eye on the Level of water, as you open the Analog Tap, which is an equivalent of a Motor operated Valve. Your Eye is an advanced Optical Sensor, which is able to sense the level by the computation in the brain, which in turn operates the muscles of your hand, thru the nervous system. The hand along with the Water Tap is is the Actuator. As the water fills up close to the top, you start reduction of the water flow and keep observing, then as it tops up, you tweak the tap to a trickle. When it reaches the limit you shut off the tap.

Closed Loop Control Systems

While you are half way filling the bucket, what happens if you take a short nap, or a friend comes by and you are get absorbed in conversation, the water overflows and goes waste. Then someone raises an alarm after the Runaway process happens. This is of minor consequence, but it is not so in the case of Temperature, Pressure and also many common systems like the driving of an Automobile. Remember the gears, brakes, accelerator to control and steer the car to the correct destination, a Runaway Process causes an accident.

    Thursday, December 11, 2014

    Computer Data Interface - delabs

    The PC is now an economic and common equipment at home or office. Due to Open source and GNU Linux, many professional programs and environments are easily accessible. To interface it to the real world is a step in learning Automation and Robotics.

    Computer Data Interface - delabs

    Computer Data Interface - delabs

    In Automation we have both Industrial and Home. You can start with home automation, as industrial automation is more complex. But in Home Automation, Safety First should be emphasized, Any neglect in care of electrical hazards will neutralize any advantage of Home Automation.

    Printer Port

    Do not apply voltage above 5V to any pin of printer port, ensure earthing is good, use opto couplers for inputs and outputs if you are not sure. wrong use will damage motherboard, these circuits should be used only if your basics are very sound.

    Anantha Narayan 16:16 30-Mar-07

    Analog Interface for PC Ports.
    Control Interface to PC Ports.
    Project Source - virtual-instrumentation - Examples of Computer Interface to Instruments

    Tuesday, December 09, 2014

    Dual Differential Amp - Op-Amp Designs

    The Input Impedance of this module is very high and is symmetric. This circuit can be used for strain gauges and for four wire measurements. If inputs are in mV use OP07. The merit is that it uses only 2 OpAmps yet has high differential Input Impedance.

    Dual Differential Amp - Op-Amp Designs

    Dual Differential Amp - Op-Amp Designs

    The Outputs of Opamps are low impedance but still have limits they cannot drive more than a few mA of Current into the Load. If low ohmic value loads are to be applied use external transistors as amplifiers. If inputs Vn-Vp are floating, outputs may be random or oscillating, it is good to have a bias network of 10M resistors to a potential even zero or common, this enables some Vout when input floats.

    Dual Differential Amp Tutorial xml code

    delabs Design Service and Custom Projects

    Some old examples of open custom designs. these were made to educate the customer and also study the capability  of online communication and and collaboration tools for such activity.
    Two Stage Sequential Timer Docs - 

    The circuit is a two stage sequential timer with auto reset. It can turn a Solenoid On/Off after a Sequence of delays that are preset. This is also a basic example of timer usage in automation.

    Design Documents
    All Timers are 1 - 30 Secs Analog with Presets to adjust with a screwdriver. The Switch, Solenoids and Power supply has to be via terminal blocks or plug-jacks. The PCB may be upto six Square Inches for standard DIP components but with SMD it may be smaller.

    delabs Design Service and Custom Projects

    Four Channel Temperature Alarm Docs

    The temperature in a pipe is monitored with four RTD Pt-100 Sensors, The type of probe could be Extruder RTD probes with Bayonet or Compression Fitting, Get it from Omega. To keep costs low you can choose small thin film RTD sensors, they will be fast but on rough usage may break.

    Design Documents
    The time taken to measure the temperature at the 4 points will be less than 4 seconds. An optional display of the measured temperature as shown above can be avoided by using a DMM to adjust the setpoint.

    The Analog Timer Module can be set from 0- 30 minutes. If out-a remains high even after set time a out-b alarm goes on to sound a buzzer and flash a LED light.

    Monday, December 08, 2014

    Differential Amplifier - Op-Amp Designs

    A very simple one op-amp diff amp. This amplifies the difference between two inputs Vp and Vn the low impedance of this configuration is a drawback, but can be used in analog computing. Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are canceled by this configuration.

    Differential Amplifier - Op-Amp Designs

    Differential Amplifier - Op-Amp Designs

    Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make circuit stable. For AC applications use LF351 TLO71 as they have good slew rate and also are FET inputs. For AC applications use a capacitor (1uF) in series with Ri to block DC Components. The Inputs have asymmetrical input impedance this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

    Simple Differential Amplifier Tutor xml code

    Tuesday, December 02, 2014

    Non Inverting Amplifier - Op-Amp Designs

    The input impedance of this module is very high, if U1 is OP07 it is in mega/giga ohms, use CA3140 or LF356 fet input opamps to get 1 tera ohm input impedance, but for high gains OP07 is better as it is ultra low offset. This is a good amplifier for sensor outputs, as it is a DC Circuit.

    Non Inverting Amplifier - Op-Amp Designs

    Non Inverting Amplifier - Op-Amp Designs

    The zener diodes protect the opamp inputs, R1 limits current during high voltage inputs and R1 and C1 form a filter to remove some ac components, C1 should be a plastic type as ceramic and electrolytic caps are leaky. A large C1 will slow the response time, the sum of Ri + Rf should be greater than 5k so that output is not loaded. Do not connect output to voltages more than vcc/vdd, it will blow Opamp.

    Non-Inverting Op-Amp Tutorial xml code