delabs Circuits

Thursday, December 18, 2008

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.

Saturday, December 13, 2008

Capacitor Temperature Monitor

When placing sensors in high pressure or vacuum chamber, they should be terminated by an epoxy sealed terminal block interface on the system. 4 wire RTD is best for such applications, as multiple terminations and junctions are involved; also the wires may have to run some distance.

When measuring temperature in a big surface or object, use multiple sensors. An indicating scanner-controller can be used or ensure cooling-heating is uniform using fluids or air circulation.

Zoom Image

Cooling Controller


RTD Sensors to Terminal Block Connections

W - is White Wire from RTD, R - is Red Wire from RTD, Color of Wire on RTD Sensor Pt-100.
Top 3 Terminals are for RTD 1 (Red), Bottom 3 Terms. are for RTD 2 (Yel), Marked with Color Tape.

The RTD two whites go to one end of the Platinum 100 ohms resistive sensor, the red goes to other end. The red in this sensor goes to gnd of opamp circuit in controller. Thru one white a 1mA current is injected, the other white gives a voltage output to opamp. This voltage after offset and calibration is proportional to temperature.

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