Showing posts with label Process-Control-1. Show all posts
Showing posts with label Process-Control-1. Show all posts

Wednesday, February 03, 2016

RTD 3-W Mains Power 4-20 mA Transmitter

This is the Photo of a RTD 3-W Mains Powered Temperature 4-20mA Transmitter. The Circuits and PCB are here RTD PT100 Transmitter and Multiplexer.The Circuit RTD-Pt-100-Transmitter Circuit.

RTD 3-W Mains Power 4-20 mA Transmitter

We can classify Transmitters as shown below. The Measured Parameter Temperature, Flow or Events Has to reach an Intelligent Data Storage and Analysis System. It may just be an Human Operator who jots the data on a Notepad and Turns a Few Dials based on his Experience or an embedded controller. It could even be a Computer Network or a Web Application used,
  • Analog Transmitters - Like 4-20mA Loop.
  • Electrically Isolated Analog Transmitters.
  • Transmitters that need to be Intrinsically Safe.
  • Digital Transmitters and Optical Interface.
  • Wireless Transmitters and TCP-IP.
The job of the transmitter is to take the weak analog measured parameter information from sensor, be close to it, amplify, clean, linearize the signal if required and send strong - error free data over a long distance to an operator or system.

Process Control Instruments and Custom Solutions has been my core Strength. The RTD Pt-100 Transmitter with 4-20 mA output shown here was used in numbers with a 4-20 mA Analog Multiplexer. This was in turn monitored/controlled by a PLC SCADA System to monitor many points in a large Industrial Plant. The external multiplexer makes unlimited channels possible with a Standard Analog Input and Digital Output Module.

Sunday, February 08, 2015

Process Control Instrumentation

This is a generic or standard controller for any type of process. Shown here is a temperature controller.

The STC1000 could be used for Ovens or furnaces, liquid baths, heating or environment chambers. It has a single analog input and an analog or relay output.
Temperature Controller

Process Control Instrumentation Section Updated

Analog inputs could be like 4-20 mA, thermocouple or RTD. Analog outputs can be 0-10 V for a thyristor drive, SSR drive output or potential free contacts of a relay to operate external 3 phase contacters.

The closed loop control could be On-Off or Time-Proportional. It was known as digital temperature indicating controller. Sometimes it would be used just as a Alarm or in a Trip circuit for protecting a system, when a uP or uC based PID controller fails.

This is used in the processing of plastics, rubber, metals and in chemical plants too. Here is a checklist that was made for helping its fabrication. You can see the limitations in which we manufactured these products. An optimum quality was evolved, defined by a user's affordability of the product.

Thursday, February 05, 2015

Process Control Circuits for Automation

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

Industrial Process Control Circuits has been updated.

3 Wire Transmitter

Circuits in process control
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.

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.

Thursday, November 20, 2014

Thermocouple and Pt-100 RTD

The easiest way to measure temperature is with a glass diode like 1N4148 or a metal Transistor like 2N2222. These have a small temperature range, probably -5 to +120 is possible, but non-linear. A copper coil or any metal wire or even a wirewound resistor can work as temperature sensor but the thermal inertia makes it sluggish. IC semiconductor based sensors like LM335 and AD590 are easy to work with and pretty accurate. In industrial environment many types of Thermocouples, Pt-100 RTD and Optical Infra-Red Temperature measurements are used.

Input Levels for Thermocouples and RTD Pt-100. And the ways it has to be used. Thermocouples are selected on the basis on how they are mounted or fixed, the environment, the temperature range that is measured and finally the price you can afford for a particular application. Sometimes mechanical wear or chemical environments may eat away the sensors, so a cost-effective solution has to be evolved.

One customer wanted a special Pt-PtRh very high temperature sensor for molten aluminum. It was very difficult and costly to even arrive at a solution. So a non-contact infra-red sensor may save lot of time-money and even reduce risk of injury.

Thermocouples and RTD Tables

For J, K, and T Thermocouple Read "Temperature" + Room Temperature for mV shown applied to equipment, eg....

If Room Temperature is 25 Deg C and mv applied is 10.777 for J Type STC1000 then reading should be 200 + RT = 225 deg C. The mV shown are for Reference Junction at 0 Deg C.

It would be better if you refer links below, The above table i made long ago, then a Scan with OCR later formatting. It could have errors.

Read More

Thursday, March 06, 2014

The Evolution of Temperature Control

A closed loop controller is the heart of an Industrial Automation System. Right from an On-Off Hysteresis Controller to a Auto Tune PID Controller, we find solutions of different complexities. Each solution might suit a particular system; depending on the requirements of Ease-of-use, Cost and Process Type.
Evolution of Temperature Control
  • Bimetal Thermostat
  • Analog Dial On-Off Controller.
  • Analog Dial Proportional Controller.
  • Digital Display - Analog Controller - On-Off.
  • Digital Display - Analog Controller - Proportional.
  • Digital Display - Analog Controller - PID.
  • Microcontroller Based Process Controller. (On-Off, Prop., Universal TC, RTD, mA Input)
  • Process Profile Controller (Microcontroller Based).
  • Microcontroller Based Fuzzy or Auto-Tune PID Controller.
  • Data Logger, Computer, PLC or SCADA based Solutions.
Even today, the controllers at every stage of evolution, from the thermostat to Auto-Tune, are used in many countries, for many different industrial applications. No solution above is obsolete! The developing Countries still use electro-mechanical or semi-automatic means for control in some areas.

The Evolution of Temperature Control
 A PC based multiplexed scanner controller with data-acquisition cards and I/O Cards can be solution for Laboratory or Research. This is used when real time control is not required or where the control failure will not lead to damage or loss.

A PLC or Microcontroller based controller should be used with a Analog Controller Protection or Over temperature Trip-Alarm.

Outputs could be Relay or SSR, Voltage and Current outputs like 0-10V and 4-20mA are needed sometimes to drive DC/AC Drives or to control Motorized Valves. Relays and SSR can be On-Off or Time proportional (PWM). The Cycle times can be 10-20 Secs for Electromagnetic Relay and around 1 Sec for SSR. This is because Mechanical Relays and contacters have limited number of operations. The zero crossing SSR has to be cycled slower than mains frequency.

In Curing rubber, which is one of the more complicated process, we need a profile based controller, which also triggers other timers or counters which need to be activated at different segments.

When a very big area is controlled, with materials or load placed un-symmetrically, Every corner or section has to have separate sensor and controller. These are then governed by a SCADA, Supervisory PLC or Master Controller.

Industrial Process Control Circuits

Even a Big Die for Plastic Moulding with an Unsymmetrical Object or long object to be moulded; needs compensation for sides which will absorb more heat.