Wednesday, February 11, 2009

Proportional Temperature Controller

Proportional Temperature Controller
This is a Proportional Controller where the setpoint is derived from a Thumbwheel switch.
Proportional Temperature Controller
The conversion of Thumb-wheel Digital Data to Analog mV is similar to R-2R Weighted Resistor Network. In this case it is a 1-2-4-8 Binary Weighted Resistor Network. It has no Digital Components.
You can see an example circuit below for digit weights you just use like 10K-100K-1M etc. There is a problem of procuring 8M Resistors, so use series parallel combinations, avoid open presets. Trimpots can be used but then it raises the BOM cost.
1-2-4-8 Kilo Ohms may load opamp for high output levels. 1-2-4-8 Mega Ohms may be ok in the lowest digit. Greater than 10M designs are possible only in lab, not in commercial or industrial domains.
Binary Weighted Resistor Network
Make such R networks, solder array on thumbwheel, in some thumbwheels remove diodes or other connections. Club all of them, thumbwheels. One opamp will do. Use -2.5 V for positive mV output. The resistors should be close to 0.3% at least.
This Binary Resistor Network can also work with Digital CMOS Chips like CD4029. Use these chips on a separate supply, which is just a LM336 - 5V device. A digital thumb-wheel also can be used.

In this controller you can see a sensor open indication. When the sensor breaks, the temperature controller may continue to turn on the actuators or heaters, It may even Oscillate. So when a high impedance is detected in the sensor input terminals, the output relay is shut off and a LED is turned on to simplify operator's diagnosis.
Mount the controller a distance away from heaters, ac-drives and vibrating parts. Avoid direct sunlight on controller, fix controller in a sealed control panel. Earth the point where the thermocouple senses heat. Some heaters leak. The machine has to be earthed.


Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits

Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits

Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07

Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition

Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent

Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525

Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments

Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors