Design of a ADC Interface

(Summary) This is in continuation of the thread called "Design of a Thermocouple Amplifier" doc00023.html which is in the same section .

This is just a formatted-edited email thread exported from Eudora from my mailbox using the content concentrator. The circuits below were made by TF a student, This thread has been put online to share information.

The part under "From: delabs" are my writing. there may be some mistakes and broken links.

Datasheets -  AD590 from Analog Devices - - MCP3002 from microchip.com

Circuits Drawn by the Student.

1. ADC Circuit.

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2. Power Supply Circuit.


From: TF

Now I will start working on the CTC and the ADC part.

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From: delabs

Now it looks ok, use bases for all ICs, which ADC you are using ? Try to look at LTC1298 a 12 bit 2 channel, look at link below....

8051SBC V1.0 - Microprocessor learning board demonstrates exemplary design of 8-bit singleboard computer. More peripheral and easy to adapt to be a dedicated controller.

Read the Full page - Design of a ADC Interface for Microcontroller. - Fulll

Design of a Thermocouple Amplifier.

(summary) This is just a formatted-edited email thread exported from Eudora from my mailbox using the content concentrator. The circuit above was made by TF a student, This thread for circuit above has been put online to share information. The part under "From: delabs" are my writing. there may be some mistakes and broken links.

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1) Reg diagram STC1000A :
Is the reference voltage REF used for cold temperature compensation ?
2) What is the function of q1 and q2 transistors ? Are they also BEL100N ?
3) What is the function of VR2 ?
4) What is the function of P2 , P1 ?
5) How can I calculate the voltage at the output IC2A?
6) Is is possible for you to send me a circuit explanantion which will help me to understand all the circuit operations ?


The circuit stc1000a.pdf is here name is "temperature controller, j and k input, pdf"

From: TF

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REF is pin no 13 in header of the connector CON1 of board STC1000A. The CON1 of STC1000A is plugged into CON1 of STC1000B main board. it goes to Stable Reference LM336 2.5 IC2 of STC1000B, the entire STC1000x series is a set. RT1 is for cold junction compensation, see how to build it in dact0006.pdf .

Q1 and Q2 are BC547 small signal NPN, The act like crude attenuators with the resistor networks. This circuit is to linearize the output, study other circuits in my page you will understand. When the analog voltage becomes a bit more than 1% off from a line the switch can be put on. You can even use things like CD4066 and other analog switches but it will increment the cost. IC2D is just a differential opamp circuit see theory.

This amp switches the transistors to linearize output at an area determined by VR2. P1 and P2 are for 'zero' cold junction and 'full scale' calibration, these are given in the theory section. IC2A is a buffer there is nothing to calculate, read the theory here you have to study many of the links i post and also many other links to other sites, that will help you more.

delabs

Read the Full Page - Design of a Thermocouple Amplifier Full

Testing Points and Pilot Production

Some Pilot Production And testing points when building electronic Projects.  These are also important while prototyping and Bread-boarding. These are things that i used to keep telling youngsters when they are new in manufacturing. This was when i was running my own firm making industrial equipment and instruments.

I used to even give this and some other pages around in printed format, it was composed with word on windows 3.11. Then i realized it has to instructed at every incident by example. Reading does not help unless someone is passionate and enthusiastic about learning.

Tutorials on Basics and Instrumentation



Components

• Use 1% MFR 100 ppm resistors for all analog instrumentation.
• Use plastic or-and multilayer capacitors as ceramics are leaky.
• Product should have minimum number of fasteners.

Assembly

1. Nuts, Bolts and screws locked with adhesive so that they do not slip and the product falls apart.
2. Potentiometers should move smoothly and not get twisted, strained or locked due to cabinets.
3. Use Strain relief for wires and strip the wire and solder properly where required.
4. Strip with a stripper do not use your teeth., Twist all the strands Tin the tip of the wire.
5. After Tweaking and setting presets or trimpot lock it with paint or varnish.
6. Big Components should have large pads and separate mechanical fixing to PCB.
7. Acrylic and plastic can get blurred or deformed with some solvents.

Testing
Do assembly of the card with a tested assembled 3D reference. Even after all the care if the card does not work, then after full assembly do visual inspection in this order First keep both the cards one reference and the other manufactured under a bright light.

• Compare resistor color patterns one by one.
• Compare Electrolytic capacitors physical appearance and POLARITY.
• Verify values of plastic and ceramic capacitors.
• Cross-check Diode sizes and POLARITY. Verify Zener values.
• Check IC and Regulator POLARITY and Exact type number / brand
• Check Transistor, MOSFET, LED, POLARITY. and verify display type No. and Polarity .
• Check for connector patterns and polarity and switches etc.
• Reverse the card and Check for solder bridges between close pins .
• Reverse card and Check for hairline shorts and solder streaks due to bad PCB processing or Soldering.
• Reverse card and check for hairline cuts or pads lifted off card.
• Closely observe for dry solders on big electrical parts (L and TX) a dry solder will cover the pin and will be dull in shine.
• before calibration allow for product to warm up for 15 mts.

If all the components were subject to incoming inspection and testing. If still unit does not work remove power and do cold check comparison with reference unit in DMM 200K R range, if still problem persists continue with power on testing and solve by DMM or scope tests.

Danger ! when DMM is in Ohms Mode, Even if one probe touches 230 V, DMM is Gone, so take extra care while doing this. test probe.

delabs Technologies

First written and printed offline in the Nineties. Word on Windows 3,11 with Epson 24 Pin Dot Matrix Printer., updated 2014.

Electronic Tables and Charts

How to Test Verify the Testing Methods Itself

Testing and Evaluation tools must have dynamic decoys added into the device under test DUT or the batch under test. In a Conveyor system, identifiable (RFID) decoys must be artificially introduced every 100 pieces. This will constantly counter check the Testing system and in not a One time operation. The decoys should be defective or have a fault, a little above threshold. This is caught by the testing system. Even when the testing system ages or goes out of calibration, this method can raise a alarm.

Even in software and text/data processing; this method ensures database quality and software program integrity.