Control system design Notes

Proportional Controllers not only save energy, they can give a controlled finish or treatment to a job. An on-off controller or thermostat limit protection has to be used in series, this is to to stop a Runaway Process.

control system design

There was a real life instance when a Temperature cycling oven maker (environment chamber), faced large liabilities as an 8086 based profile controller and chart recorder just locked up and all the electronic equipment were roasted. Here even a bimetallic thermostat would have saved the day. Nowadays we have a watchdog timer to prevent such uP mishaps, but still use an analog controller in series as an over temperature trip.

Other Reading

The basics of control system design: Part 1 – Moving beyond PID

“This series of six articles will explore the use of six variations of P, I, and D gains: Proportional Control, Proportional-Integral Control, Psueodo-derivative feedback with feed-forwared (PDFF), PID control, PID+ control, and Proportional Derivative Control.”

Mini RTD Pt100 Three Wire Transmitter

These are the circuits and boards of a Mini Temperature Transmitter for a Platinum hundred ohms temperature Sensor.

Transmitter RTD

The customer wanted a two wire system, this needs low power opamps which were ten times the price. If this transmitter works at 3mA it could have been two wire. Those parts were in short supply and the budget of customer was low. So i made it with regular opamps but three wire. The customer was satisfied as he got a cost effective solution. But now the situation of markets and products are different.

RTD  Three Wire Transmitter

If you need to transmit the temperature from a high voltage area or toxic environment. You will need to hermetically seal the transmitters, convert the Voltage to frequency, frequency to IR LED flashes or RF. This can be then remotely monitored. Then the transmitter has to be battery-solar operated, low power too. ICL7135 is a simple solution. It has a serial output that can be used to Drive IR Leds. Remotely sense these flashes in a Micro-controller and you have a reading. You may be able to use optic-fibers too. Where volatile liquids are present so that the risks of sparks can be eliminated.

3 Wire Transmitter RTD

More at Process Control Circuits

This is the same Mini RTD Pt-100 Transmitter but in its case. Encapsulated in epoxy, hermetically sealed against harsh industrial environment. This will work well even near fumes of Ammonia with no corrosion. But not near vapors which can be ignited by sparking as terminals are still open. The side view shows zero and full scale ten turn bourns trimpots heads, for calibration. After cal it can be sealed with RTV compound.

3-1/2 Digit ICL7107 DPM Digital Panel Meter

This is a Digital Panel Meter based on ICL7107. This was the workhorse Digital Readout chip before Low power uC designs were developed. Even now it is the easiest way an analog parameter can be displayed in an instrument.

Instrumentation and Measurement Circuits

3-1/2 Display is just enough resolution for recording process data or troubleshooting equipment. With 4-1/2 you notice the problems of thermoelectric EMF of probes and connectors. That is one reason gold plating is used another being low contact resistance. In 4 1/2 the reading can change due to contact resistance too, if the input impedance of the analog signal conditioning is low or the protection diodes, RC filter caps are leaky.

ICL7107 DPM Digital Panel Meter

When you measure an analog parameter from a sensor; you attenuate or amplify it, to scale to the A/D converter range. You also need to protect or isolate the analog front end from high energy mis-connections, which will happen during field use. The operator should not get injured from any high energy leakage while measuring.

Resolution is the finest detail you can enumerate in a parameter or object. You can say the crowd was 3000 or 4000 people. Here 1000 is the resolution, finer data does not matter here. You would also hear things like, there were 80 to 90 boys in that classroom. 10 is the resolution there.

Accuracy is how precise a statement or number is. If there was 85 boys in that class, the above statement is accurate. If there was 65 boys, the measuring method or process needs calibration or examination.

In this circuit, the plastic caps should be of very low leakage. Multilayer plastic caps are good for instrumentation.

Equipment Control using Embedded Internet

I will give a simple example for the purpose of understanding and assimilation of the concept. Consider the Toaster a Vital Home Appliance, Build a Embedded Internet Interface into the toaster. Then make it Wireless Networking capable. The gadget can also get connected thru Mains Carrier Communication.

Now you build a Webware service, create API’s, Ready Gadgets and Wizards. So he can create-use the API from any Computer or PDA. He can Sub-Lease his custom API Service with Internet capable Gadgets.

Make this a Web Toaster – When i made this post, the iGoogle was the reason behind it.

Make this a Web Toaster

When the Javascript of this is linked to the API of the Control Webapp that you created, This gadget can monitor and control the Quality of the Toast from anywhere in the world ;-).

Digital Timer for Internet – Live Widget

But Then, the service should be easy for just anyone to use, the coding is never done by the user of the service. He creates an account, hires the API, creates his own Gadgets and Apps with wizards. Then he gets to download the firmware for the Embedded Internet ASIC you Provide and the Product he manufactures goes with that circuit. See a Screenshot below


The end customer buys an Internet capable Toaster with a CD demo on how to access his free webservice. With this service, he can get all the web gadgets and tools to control his Home Appliance Arsenal.

Idea – 19:36 25-Feb-08, Nature – Open Source, – Ideas of delabs

More Reading –

Future of Industrial Automation and Process Control

Automation and Control is the predecessor of Robotics. A Jump Start, Practical and standard reference for Process Control is at at Omega Technical Reference.Tacho Counter

A Control system is made of Sensors sending acquired data to a Controller which operates Actuators to manage the process in Real Time. Starting from a Bimetal Thermostat to a SCADA, the controller has grown from mechanical — electrical — analog — digital devices to microcontroller-computer based equipment.

Both in Control Systems and Robotics the Collaboration between Robots or Control Units, leads to the development of wireless network of Interactive, Intelligent and Distributed Self Governing Systems. The outcome is Web Process Automation, Web Applications based Solutions in Monitoring, Analyzing and Configuring these Sophisticated Networked Systems.

Read More at my – Industrial Process Control Applications

RTD PT100 Transmitter

This is a RTD Pt-100 Transmitter, It can Convert Thermocouple mV or RTD mV to 4-20 mA Current Transmitter. The part numbers on Circuit and silk screen may not match. But the PCB may be usable. The output is a current source and not a current sink. It goes to a 4-20mA Mux with a common ground. The Circuit RTD-Pt-100-Transmitter Circuit.

RTD Transmitter 4-20 mA

This low-cost transmitter was made to send RTD information in a 4-20mA over long distance. The 4-20mA was the input to a Analog-Mux which interfaced to a GE-Fanuc PLC system and a 486 Computer. The Analog Multiplexer Built around CD4051 was was controlled by PLC to get data from numerous channels. This reduced the cost of the System. This is ok when Real-Time Acquisition is not required. The Analog 4-20 to 4-20 Mux-Buffer circuit can be seen at Industrial Process Control Circuits.

This was done as customer budget could not afford dedicated analog input modules for every channel. There were more than 50 Inputs. The thermal inertia of system did not need a real time or fast correction.

The PNGs of PCB is 600dpi 16 color. It is to be scaled appropriately.

ICM7217 Preset Counter with 4 Digits

ICM7217 is a four digit, presettable up/down counter with an onboard presettable register continuously compared to the counter. The ICM7217 is intended for use in hard-wired applications where thumbwheel switches are used for loading data, and simple SPDT switches are used for chip control.

Digital Timers, Counters and Clocks has some of my designs using chips like this.

This circuit provides multiplexed 7 segment LED display outputs, with common anode or common cathode configurations available. Digit and segment drivers are provided to directly drive displays of up to 0.8 inch character height (common anode) at a 25% duty cycle. The frequency of the onboard multiplex oscillator may be controlled with a single capacitor, or the oscillator may be allowed to free run. Leading zeros can be blanked. The data appearing at the 7 segment and BCD outputs is latched; the content of the counter is transferred into the latches under external control by means of the Store pin.

See an Application of 7217 as a Preset Counter which is used in Process Control

ICM7217 Preset Counter

Features of Chip

  • Four Decade, Presettable Up-Down Counter with Parallel Zero Detect
  • Settable Register with Contents Continuously Compared to Counter
  • Directly Drives Multiplexed 7 Segment Common Anode or Common Cathode LED Displays
  • On-Board Multiplex Scan Oscillator
  • Schmitt Trigger On Count Input
  • TTL Compatible BCD I/O Port, Carry/Borrow, Equal, and Zero Outputs
  • Display Blank Control for Lower Power Operation; Quiescent Power Dissipation <5mW
  • All Terminals Fully Protected Against Static Discharge
  • Single 5V Supply Operation

delabs Notes-

This is another Intersil Masterpiece in days when using uP was complex and uC was not available.A 8085 could be used but with many supporting chips and it consumed power. This was a CMOS innovation low on power and just one ASIC had the fexibility for many digital operations.A ThumbWheel and Display Interface completed a Gadget.