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Blind Dial Analog Temperature Controller

This is a Low cost controller, Analog Dial Temperature Controller. It is also called Blind Controller. This essentially means Open Loop, just control the fuel or energy input to the system to regulate heat. This is not a Blind Controller that way, it only cannot display the temperature value, that could be another reason it is called blind.

Dial cyclic timers were used to control heat, these were purely mechanical clockwork devices. They could regulate well, when the material flow (liquid) is constant and mains power is regulated. But when the job to be heated, varies in quantity, control temperature is close to ambient or when a precise control is required; closed loop controllers are used. Even a thermostat is like closed loop, as the bimetallic sensor is temperature dependent. But not good enough.

This controller is closed loop, precision controller, only the digital display of temperature is absent. Fine one deg variations may not be easy in this.

Blind Temperature Controller

PCB Boards for Blind Controller –

Discussions –

Wandel and Goltermann – Communication Instruments

Just like Rohde and Schwarz which is a world leader in Communications Test Equipment, There was another from Germany called Wandel and Goltermann which made specialized RF Test Instruments.

A short history is Wandel and Goltermann became Wavetek Wandel Goltermann (WWG) and then Acterna, Now it is a part of JDSU Communications Test & Measurement.

See also Willtek Company History

Here are scans of a old catalog of Wandel and Goltermann.

Wandel and Goltermann

From Electronic Catalogs

Brief Introduction of WG

From Electronic Catalogs

Thermocouple Temperature using DPM or DMM


Description –

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.

Going to practical temperature measurement, we know that one of the junctions is the sensing or hot junction (Tmes) and the other junction is the terminating or cold junction (Tref), the voltage between terminals ‘a’ and ‘b’ is proportional to Tmes – Tref (and given in the Table 1) . The formula being Vab = alpha x (Tmes – Tref), where ‘alpha’ is the Seebeck coefficient of the thermocouple.

Thermocouple Junction

Table 1

MV Thermocouple
Temperature in Deg C As cold junction is not zero but is at room temperature (RT) add RT to temperature.
0 0
2.585 50
5.268 100
10.777 200 Example –

Feed 10.777 mV to the TC+ and TC- terminal if RT then is 30 Deg C reading on 2V DPM Will be 230 counts – 230mV.

16.325 300
21.846 400
27.338 500
33.096 600
Reference junction or cold junction at 0 deg C.

In the circuit, use only metal film resistors (MFR) of 1 per cent tolerance, as this is an instrumentation application. Power supply should be a stable +5V, -5V supply, for which one can use 7805 and 7905 regulators.

The inputs TC+ and TC- terminals should go to a 4-way barrier terminal block, the 2 extra terminals are used to mount TH1 Cu thermistor. This forms an isothermal block, which is good enough.

A simple way to make a TH1 Cu thermistor, is to take a 1 Meg-ohm 2W resistor as a former and wind 2 meters of 46 SWG enameled copper (Cu) wire (5.91 ohm/meter) over it. This gives a 12-ohm value. Terminate wire ends on resistor leads.

Circuit Diagram –

Thermocouple Temperature using DPM or DMM

Thermocouple Amplifier Circuit – PDF version of above, more details and easily printable.

Test and Calibration –

For calibration, you will need a DMM-DPM and a milli-volt source (as shown in the Fig.). First connect source to terminals TC+ and TC-, then set source to 0.00 mV (verify with DMM for zero). The output across +out and -out (use DMM) terminals must be mV representing the room temperature (RT). For example, if RT is 30° C (use a glass thermometer) then +out should be 30mV at 0mV input. Adjust VR1 till 30mV is read at +out terminal. This is ‘zero cal’.
Millivolt Source
Now increase mV input to 21.85 (corresponding to 400° C). Now vary VR2 till +out terminal is at 430mV (temp. +RT). This is ‘gain cal’. Now as VR1 and VR2 are interdependent you may have to repeat ‘zero cal’ and ‘gain cal’ a few times till you get the above values.

Properties of J thermocouple and design aspects of gain block used in the temperature measurement instrument are summarized below:

J Thermocouple Ansi Symbol ‘J’ –

  1. J is a thermocouple made of iron + VE and constantan -VE.
  2. Constantan is an alloy of copper and nickel.
  3. Full range of use is from -200° to +700°C
  4. Practical to use only from 0°C to 400°C.
  5. Useful in reducing and Alkaline atmosphere.
  6. Corrodes-rusts in acidic and oxidizing atmosphere
  7. Color code of wires negative-red and positive-white.
  8. J type is popular because of Low price and high mV output.
  9. J type TC used in rubber-plastic forming and general purpose use.

Design of Gain Block –

  1. Minimum input from thermocouple is very low like 1-2 mV. Hence ultra low offset (100uV opamp is required – OP07 used).
  2. Inputs may be subjected to wrong connections or high voltage. Use of R1 limits current and Zener ZD1 clamps voltage to safe level. (low leakage zener or use diode).
  3. Gain required is 400mV – 21.8mV that is approx 18 at 400° C. Gain Av = ( Rf + Ri ) / Ri here Rf is R7 and Ri = R5 + R6 + VR2 (in circuit value).

Design of TH1 cold junction compensation copper thermistor –

J Type TC output changes by 0.052mV per deg C as per Table 1. Copper has a temperature coefficient of 0.0042 ohm per ohm/deg C. eg. for a copper wire of 12 ohms, it is 12 x 0.0042 = 0.05 ohm/deg C.

For R1 of 5K current Thru TH1 =5V / 5K = 1mA. Change of voltage across TH1 with temperature is
0.05 x 1mA = 0.05mV / deg. This rate is same as J type TC hence it simulates cold junction

Anantha Narayan

Analytical Instrumentation Technologies

Electrical Engineering as a Technology has evolved and branched out into many specialized domains. With the coming of Semiconductors and the Advancements of Material Technologies, Electronics Engineering emerged as a foundation or a Horizontal for many new Verticals.

Analytical Instrumentation Technologies

One such Vertical is Instrumentation, here you know Industrial Process Control is one and the other is Test and Measurement. The third branch we learn about today is “Analytical Instrumentation Technologies” which is more like an Oblique, it Cuts thru Physics, Chemistry and Biology and many of its sub-branches. It also supports the areas called Life Sciences, Bio Technology, GeoSciences, Materials Science etc. .

Here i have posted some analytical instruments … Laboratory Analytical, – Research and Lab Instruments, Bio and Earth Science. – EEMetric.com – Test and Measurement Instrumentation.

Start Learning –

(I Inherited some chemistry apparatus and chemicals from my grandfather. This lead to a Tiny Physical and Electro-Chemistry lab in the Store Room and later the Garage when i was at school. That is one of the reasons my website has the name delabs and i created a blog called “Analytical Bionics” around 2004. Later those posts were integrated in my other blogs.)

Basics and Instrumentation Electronics

The Basic Tutorials Section has been updated, “Basics” in an Instrumentation Viewpoint. Some Learning i had written down, Later made a Newsletter Amps-n-Volts. Now i am organizing everything into one area. More like Content Management by chewing the cud.

Digital Multi Meter – New Year Resolutions Fluke Electronics - DMM

  1. I will not drop the DMM from a height of 4 feet.
  2. I will not Test Live Powered equipment in the Ohms Mode.
  3. I shall not Measure Mains Voltage in The Current Mode.
  4. I shall get it calibrated once a year or at least once a decade.
  5. I shall not use it in High Energy Measurements.
  6. I will try my best not to give it to my best friend.
  7. I can remember Red is Positive and Black is negative.
  8. I will wear shoes and stand on a block of wood while i test.
  9. I shall not operate the rotary range switch at high speeds.
  10. I shall replace the probes-cables-connectors on wear-tear.
  11. I shall not accidentally keep the hot-iron near the DMM or leads.
  12. I shall not keep DMM on tall table and pull it with the leads.

DMM – How it Looks … shown right is from Fluke Electronics
How To Learn Electronics :

Theory must be studied once and referred to, again and again as you do practicals. One is by building DIY projects and then modifying them. Also Repair of equipment, troubleshooting, testing and calibrating. Then you know how components behave and real life limitations. Now design and engineer a product and test it at customer site. do a pilot production and test with more clients. Now you will learn to think based on practical applications.
Guide

“with hard work and innovation you can do it ! “ Solderman Talks 1702 AD

Solderman Talks 1702 AD

Optical Retro-Reflective Proximity Switch

This circuit is used to detect objects by reflected infrared light. It can be built into a cylindrical enclosure just like an inductive proximity switch. This is also useful as a level detector for colored liquids like oil. This has some immunity to ambient sunlight as it detects ac pulses.

This is a Hand Crafted PCB Artwork done by a PCB Vendor years back, this method may be used even today.

Optical Proximity Switch - PCB

PCB Design –

This Layout may have many jumpers and may need to be cleared of Hairline shorts which has happened after i scanned it, cleaned it and enhanced it using image manipulation software.

This PCB would go into a 30mm Nickel Plated Brass threaded tube, with Epoxy or Teflon ends. These were turned components as quantities made were small. An Optical Proximity Sensor that would fit the same place as the eddy current or Inductive sensors, in existing machines. It could work a longer distance and could detect Non-Metals and even translucent fluids.

You can design your own PCB with CadSoft Eagle Layout Editor. Laser prints of output works well, but even Ink Jet printouts will work fine for small PCB’s like this. Take 3x or 4x prints.

Flow Measurement and Control

There are three Controls to be Adjusted to make a Proportional Flow 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 Flow or Velocity of a Fluid.

1. Set Point. (SP)

This is the Flow Rate at which you require the Fluid to be controlled at. Adjust the rate at which the fluid flow is expected to be controlled .

2. Process Value. (PV)

This is the Actual Flow Rate of the fluid in the flow sensor or its path. It is very important that the Flow Sensor is placed at a position in the fluid circuit in such a way to avoid cushions which may lead to oscillations around the Setpoint.

3. Proportional Band or Dead band. (PB)

Dead band or H % or Hysterisis are terms used in on / off Controllers in proportional controller we use the term proportional band.

4-20mA Control Signal

The Flow rate zone in which the Output is 4.1mA to 19.9mA which in turn Drives the AC-Drive >> Motor from 0% to 100% is the proportional Band. It is Given in % e.g. 50% PB of 200 lph SP is 100 lph. Band 150 lph – 250 lph

eg : The Motor is at 100% Drive ‘on’ till 150 lph and ‘off’ above 250 lph. ` Between 150 to 250 is the PB. A little above 150 the Motor reduces power gradually till at 250 it turns off. When SP=PV the output is 12mA (ideal) here the motor runs at 50% of the total power.

Selection of Motor / Drive and circuit Capacity:

The Motor / Drive Combination must at 12mA Control signal give a flow Rate at which the system is used for most of the time this gives good stability. The max flow rate setting required by system must be achievable at 80% of Motor Time Axis Power this is to make allowance for load and line regulations. The Flow Circuit should have normal resistance to flow to reduce Oscillations.

STC1000PFC – P = Proportional Control, F = Flow, C = Current Output.

Zoom Image

Flow Measurement and Control

Tuning or Adjusting a Proportional Flow Controller

Step # 1

Ensure Flow Sensor Output 4-20mA is properly connected to the Flow Controller polarity reversal will show reducing reading in the Display as Flow rises. The Motor / Drive used and Power selected must be able to bring the Flow more than the maximum required Flow rate directly without control (open loop).So when in doubt connect motor/drive and run at max power and observe maximum flow rate e. g. if max. flow obtained with Motor at 100% Power (direct) is
300 lph the STC1000PFC can control flow rates upto 260 lph.

Step # 2

Keep PB in middle position and power on system e.g. set Flow rate to 200 lph. Now Observe maximum overshoot. and adjust proportional band as in table. (PB Control is a 300 lph Single Turn Control with Ends.) SP 200 lph, PV (Process Value).

PV overshoot Proportional Band
10 % 220 lph or more Near Maximum fully clockwise till end.
5 % 210 lph to 220lph Middle of the PB Control or towards max.
2% 204 lph to 210 lph Little above present setting.
Less than 200 lph Droop e. g. 190 PB is Critically set Do not Change.

After each change turn on system again to see response till 2 % or less variation or overshoot or oscillations are obtained.Flow Control Curve

Thumb Rule ! –

  • Increment PB to Decrease Overshoot.
  • Increment PB to Decrease Oscillations.
  • Stop adjustment when PV droops around SP with no oscillations.
  • Adjust EC to match SP = PV after PV is stable at a point less than SP.

If proportional band setting is maximum, fully clockwise turn till end (single turn pot) the motor will slowly ramp up to full flow speed and ramp down slowly to reduce flow.

If proportional band is at the minimum, the motor will go full speed till it comes close to the set flow rate and turn off abruptly almost like an on / off controller the motor may pulsate on & off near setpoint.

Step # 3

There is an additional control called Reset or Error Cal EC ( Integral) which is factory set for SP=PV 50% Power Output i.e. Output Control = 12mA. In certain cases after stable reading is obtained after adjusting or tuning PB the Flow may stabilize say at 195 lph for a set point of 200 lph the process is stable but a ten lphrees process error is present. this can be Corrected with EC or RESET POT at the rear panel (this is a endless 10 Turn Pot).

Adjust Error Cal provided in the back panel to increase Flow rate to 200 lph from 190 lph. when this is done give some time for system to respond after every 1/2 a turn 180 lph of the RESET (EC) control pot .

The RESET control is a Ten turn potentiometer like the SP potentiometer after 10 turns the direction of turning must change. Clockwise Increases Flow rate Anticlockwise decreases Flow rate. (at min. PB setting EC pot sets the On / Off or Operating Point).