Temperature Controller Main Card

This contains the Main card with a Power Supply and Relay Control. On this card is connected the Display ICL7107 – Temperature controller.

The Thermocouple and Control Modules can be plugged into this card, these change the type of control and type of inputs. This way this can be made into any parameter controller with any type of input and output. But it is all set in production, not configurable at site.

So even if you make a 4-20mA output Flow Controller with this, the Main card and Display card remains the same. Only the Modules change. No Connectors are used, to make it vibration resistant.

The PCB Layout is here

Display ICL7107 – Temperature controller

This is the Display Circuit and PCB part of of section Temperature Control.

The above circuit is powered by +5 and -5 from a LM7805 and LM7905 pair. If +/- 12V or +/- 7.5V is used in opamp or digital parts, then use below circuit for the DPM section.

5 V Dual Supply with Zeners

The PCB for above

The PDF Circuit for above Display Card STC1000

Single Set Point Temperature Controller

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

Production Checklist of STC1000

  1. Has Transformer been soldered properly with reinforced pads – Scrape with blade area around pad and make lead bridges to support transformer.Front Card and Rear Card must have very thick solder bridges after fixing sq. post.
  2. Is the Front and back stickers and SL. No Sticker properly stuck – In Front Sticker the holes for switch, pot LED etc. must be without Burrs file and improve. Acrylic should not have cynoacralate stains. In the back sticker there should not be any wrinkles use rubber solution (fevibond) to stick properly.
  3. Are all the Threaded parts and Plastic parts fixed with fevibond – Use Fevibond (very little) for the CJ box in rear panel all Metal screws and loose mechanical parts in Pots, plastic threads and pillars. This prevents parts from breaking loose during transportation or vibrations, All Nuts / Bolts fix tightly .
  4. Are all the Pots. Turning freely and is direction proper – Clockwise is always increment or increase in a parameter and anti-clockwise is decrement of any control or parameter. All pots should turn without friction.
  5. Are all the Front panel components Fixed properly – All Four Displays are required Fourth is for Overrange and Polarity. LED’s are for Load On or Process on and Should be neatly visible above sticker and Switch should not get stuck after cabinet is closed and screwed.
  6. Only two screws must be visible on the back panel – Cover Pot clamp screw, card fixing screw etc. by Black insulation tape.Use Ni. plated Phillips / Universal head Screws for fixing back plate.
  7. Are all other items in the final packing – Check by fixing both side clamps and file if required add Instruction manual in Cover or with Invoice and DC.
  8. Sources of omissions and neglect checked by Visual Inspection – Gnd to Earth Capacitor to be added 0.01uF 103 1kV, Relay OEN only, Polarity of Electrolytic and diodes , Regulator tab touching any conductor, Loose wire strands, Solder Bridges absent at places where it is required.
  9. Troubleshooting when a card does not work – Keep always a 3D reference of a working unit / card compare component to component by visual inspection wrong polarity of diodes / Tx / IC, wrong value of Resistor or Low value capacitors missing jumpers solder bridges or hairline shorts at edge of board or pad to pad lead streaks.

Two Setpoint Temperature Controller

A Two Point Process Controller or Temperature Controller would look like this. When a High-Low Alarm Protection for uC based Controller was needed the same was modified and used.

Sometimes uC based instruments just forget and that can be costly, the watchdog timer has solved this problem. In Industrial Process Control we cannot take any chances, so a two tier or even three tier protection is required, especially so if the Job or Raw material being processed is expensive. So Real Time Analog Trip + uC Controller is safe. Then you can still have Electro Mechanical Devices for Extra protection against Fire or Meltdown.

Two Setpoint Temperature Controller

Temperature is the most common process parameter, Pressure seems to be next. Flow, Level, RPM, Distance and many more follow.

When a physical parameter let us say distance is measured, we first need a sensor that converts it into electrical values, digital or analog. The sensor used for length is a Linear encoder and it creates the electrical information for the DRO to Display.

Now many sensors like a strain gauge produce very low and weak signals and some are non-linear. So the signals undergo Amplifying, Temperature compensation and Linearizing together called Signal Conditioning. This stage outputs some standard values like 4-20mA, 0-10 V, 1-5V, or even directly digital or wireless in the new technologies. Even when a digital interfacing standard is used, amplification and some signal conditioning is required at sensor end. Compensation and Linearizing can be better done with a uC using Math or Look up Tables.

When you have many different parameters then it is better to use process controllers with a 4-20mA input standard. Then the inventory of controllers can be reused for any process.

It is always better to use sensor-end transmitters to get 4-20mA to your Controller, Recorder or SCADA System.Weak signals are corrupted by noise and dont travel long wire distance. Junction EMF at joints and terminal blocks add to errors. These are overcome by the 4-20mA signal that has the juice and punch to transmit the data over the shop floor to the control panel rooms.

Read more here Temperature Measurement and Control