LM335 Cold Junction Compensation

 Process Control  No Responses »
Nov 242011
 

Temperature Sensors like Thermocouples need cold junction compensation as a part of front end signal conditioning, this is done at the terminal block where the Thermocouple wires are terminated. This design has to be more accurate and broad, if the design we make has to work well in both Tropical and Temperate Climate Zones.

LM335 Cold Junction Compensation

Another Method using a Copper Resistor

If wires of two dissimilar metals are joined at both the ends and the junction formed at one of the ends, is heated more than the other junction, a current flows in the circuit due to Seebeck thermal emf. This effect is used in thermocouple temperature sensors.

The Peltier effect is the converse of above Seebeck effect, which means that if a current is forced through junctions of dissimilar metals, the junction will generate heat or absorb heat (cooling) depending on direction of the applied emf. This effect is used to make portable and small refrigerators. Thermocouple Temperature DPM - DMM

Thermocouple Temperature DPM – DMM

Millivolt Source with Digital Potentiometer

 Instrumentation  Comments Off
Mar 242009
 
Millivolt Source with Digital Potentiometer

Here is a Millivolt Source i built for Calibration in the early days. It uses only CMOS Digital and Mixed Chips from Intersil and CD40xx Series. Later i tried a unit with 8748 part of the code in my uC section. This is with Ramp-up and Ramp-down using only two buttons. This works even now, The support below is an HRC Fuse Holder made of Phenolic or Epoxy Resin. The mV Terminations are on Top.

Process Control Instrumentation

 Process Control  Comments Off
Feb 122009
 
Process Control Instrumentation

Process Control Instrumentation Section Updated 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. 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 [Read More ....]

Thermocouple and Pt-100 RTD

 Process Control  No Responses »
Oct 142008
 
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 [Read More ....]

Temperature Control in Plastic Injection Molding

 Process Control  No Responses »
Jun 222008
 
Temperature Control in Plastic Injection Molding

This is an Application note i used to give with my controllers – app009.pdf – Ananth Temperature Control in Plastic Injection Molding. Terms in Process Control and Explanation. There are three Controls to be Adjusted to make a Proportional temperature Controller Perform Properly. This method has to be practiced and experience gained from it can be used to get very good and stable Control of the temperature or other process parameters. 1. Set Point. (SP) – This is the Temperature at which you require the Heated area to be. Here we have to remember it is better to control the [Read More ....]

Four Channel Temperature Alarm Docs

 Process Control  No Responses »
May 312008
 
Four Channel Temperature Alarm Docs

Design Documents Discussion of four Channel Alarm. Four Channel Temperature Alarm. RTD Pt-100 Four Point Alarm. Timer and Counter Modules. Source Files Orcad Format RTD Pt-100 Four Point Alarm – 90001.zip Timer and Counter Modules – 90002.zip Block Diagram : Zoom Image Resources : Watlow heating elements, industrial heaters. Temperature Sensors. NPL Beginners Guides to Measurement – Temperature. Analog Multiplexer PT100 sensors Positive Analog Feedback Compensates PT100 Accurate Electronic Stop-Watch 40MHz Frequency Counter Module Fairchild 74C926 Long Duration Relay, up to 20 hours