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