Chirag

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.