EE442-FinalExam/Lokesh/Comments.txt

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2022-04-27 10:22:37 +05:30
Name: Lokesh
1. Question text:
Design a system using this Honeywell ammonia sensor (https://drive.google.com/file/d/164WvPD7GauvseOfH-K3v8iZ4YYmQFkq-/view?usp=sharing )
to detect when ammonia concentration in ambient atmosphere exceeds 100 ppm an alert an operator in a control room about 100m away.
This device will be mounted in various sections of an industrial processing plant. The complete plant will need a fairly large number (~20)
of sensors so unit costs needs to be kept under control. Also, once mounted it will be very difficult to remove/service/repair the sensing devices.
2. Design summary:
Your design is well thought out. Using the cascaded power supply for local boards and wireless link to control room is also a good point.
In reality you will have to check if the industry allows wireless, which bands, or whether they want some MODbus type system.
One major issue in your design is that you are using a FET as the frontend - how will you account for variations in the FET gm? Each board
will have a different gain which you need to calibrate. Similarly each sensor has a different gain and sensitivity which you need to calibrate,
you should have mentioned that.
3. Block diagram
Block diagram is fine.
Some details are missing - for example what are the protocols / signal levels between the boards?
What happens when multiple sensors go off - are there some ways to tell the control room wchich sensors have gone off?
Or how many?
4. Power supply design
Why have you chosen a rectifier supply? Can you not choose an off the shelf switching sypply?
Are you gonig to supply different PSU for every different voltage level in industry?
5. Industrial Design:
Mostly ok - dimensioning could be better. Also, are there wires coming out of the box?
Or are there connectors on the edge? or are there some cable glands?
6. KICAD Design
Schematic:
Major flaw in circuit design - your 5V regulated is not ground referenced. So any noise / disturbance in the power line will make it into the output.
PCB:
Board outline is missing and DRC fails
Why mix SMT and THT components? Also interesting that your THT components are on the back. Why?
Some unconnected stubs on your board - e.g.
2022-04-27 10:34:57 +05:30
it is good that you have used only 2 mounting holes.
2022-04-27 10:22:37 +05:30
7. Pricing / Assembly
2022-04-27 10:34:57 +05:30
Your BOM/Pricing is a little strange - why have you listed 21 LDOs byt only 2 FETS?
You need one FET and one op-amp per sensor right?
Where is the sensor cost?
What about items on the control room side?
"Protection system is wireless" ...> What is the protection system here?