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Chirag

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Chirag/Comments.txt

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Name Chirag
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:
Summary is ok. The current change is not fixed - you need to calibrate it - you have overlooked that.
On the receiver side, how do you check which sensor(s) have triggered and/or by how much?
Also, how do you handle the return lines for each sensor? You are powering all the sensors using separate isolated supplies!
3. Block diagram
System design is ok.
Lots of issues have been glossed over - what if one sensor (or its PSU) fails?
The current change is *extremely* small per ppm. What is the final current change and how do keep it immune from noise, drift, errors?
We discussed so many issues in class but your circuit has not even a mention of them?
4. Power supply design
Why use the same transofmrer for both 5V and 15V? Won't you have immense losses using a 15V transformer and 7805?
And even for 15V, your 24V rms secondary will give you far higher voltage than you need - headroom for 7815 can be nominally
5-7V even on a worst case basis to account for supply dip.
5. Industrial Design:
What is "pull" marked on the sensor box?
6. KICAD Design
Schematic:
Your part 1 has only the power supply. Where is the connector for the sensor?
Part 2 needed to be scalble - since all your processing is being done on this board you will have to make a 20 opamp version
irrespective of how many are actially deployed.
Why have you not used the correct symbol for OmAmp?
PCB:
Layut is good overall.
You have a 6pin SMD footprint for the line-frequency transformer - this shows a very cavalier approach to this design.
DRC fails on both designs, no outline.
Why is the LED pointing inwards? How will it be seen?
Your industrial design diagram has multiple "LEDs" but only one LED in the design.
No power supply indication? Power On LEDs??
7. Pricing / Assembly
There is no pricing information in the BOM and therefore no concrete justification for unit cost.
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