I have less knowledge about analog circuits. I am good at embedded programming tough. Hence i need help from expert in designing analog section in my project.
I am designing an universal data logger which is compact and has 5 inputs from various sensors (1)4-20ma current loop dc (2) 1-10v dc(3) 0-20v dc (4) thermocouple raw input (5)RTD raw input pt100/1000 input
This data logger is capable of inter switching inputs for example user can select all input to 4-20ma or all inputs to 1-10v dc or all inputs to thermocouple and all input to RTD or user can define any input to any sensor output. That is user can interchange all the inputs as per requirement.
I need help as how I can make these inputs interchangeable. Can i use analog switches or any other different technique. If you experts know or have some nice idea please help me out.
and if so Are analog switch capable of passing micro-volt from thermocouple and rtd's, can they pass 4-20ma dc current exactly without distroting .
Please help me as i am stuck from last 46 days on this design
This data logger is capable of inter switching inputs for example user can select all input to 4-20ma or all inputs to 1-10v dc or all inputs to thermocouple and all input to RTD or user can define any input to any sensor output. That is user can interchange all the inputs as per requirement.
This is an utterly ridiculous specification.
It comes across as something a complete amateur might dream up for a Kickstarter project, and use to bilk money out of unsuspecting fools before disappearing.
spycatcher2k:
Is this commercial project or college/university project?
What are you looking for? Total design, partial design, programming?
EXACTLY what hardware have you setup so far?
Sorry I didn't specified this. Yes it is commercial project and i am looking for help in partial design of analog section. Actually I work as freelancer. I use to develop small projects before and this data logger project is a kick start for me. I am given a task to develop basic design to multiplex the various inputs.
jremington:
This is an utterly ridiculous specification.
It comes across as something a complete amateur might dream up for a Kickstarter project, and use to bilk money out of unsuspecting fools before disappearing.
I'm not surprised.
Sorry sir, This is my first post in arduino forum and i dint knew the rules. Yes you guessed me right i am amateur before you expert. And yes I am dreaming for bi kickstarter project. money is today's need. But an amateur has to start somewhere. I would be glad if you guide me in my progress though.
JohnRob:
Hi,
I think we need more info about your goal and situation. With this being your first post there is a tendency to think this is not a hobby request.
Thanks for your reply. My goal is to design an commercial product . I am not good / amateur in analog section and this project exactly needs the same expertise.
project :-
This project is an universal data logger . Universal in sense it can accepts around 6 different inputs . And these inputs can interchange there position . User can set any input type to any input pin as per needs. Here in INDIA industries needs are very different. They demand for universal data loggers for cost effectiveness and easy to use.
I am facing problem as how to multiplex the various analog inputs like rtd,thermocouple. Need help Because these are sensors give very low voltage . So i am not sure whether analog switches will work or not.
Need just help for designing this analog multiplexing section
sir ,
i dont want complete design just an idea about analog switches and their switching capabilities whether they can handle very low voltages. I am not earning anything right now.I mentioned that i am stucked from last 46 days. And getting helpless i started this topic. I have to introduce my design to industry first.
I didn't hide anything. many of forum user may be making money of your inputs . Sorry once again i was unaware of this .
Thanks for input ,i will post this in collaboration.
Simple physics will tell you that mechanical switches with point or ball contacts will not operate reliably with tiny voltages. Look for switches with sliding contacts that will self-clean the contacts.
PRB_tech:
and if so Are analog switch capable of passing micro-volt from thermocouple and rtd's, can they pass 4-20ma dc current exactly without distroting .
I lke your honesty.
Analogue swithes can handle 4-20ma, but the problem is not there.
Thermocouple is producing low signal in volts (30mV ? ) which can be easily interfered by digital noise.
Use seperate voltage regulator for analoge part and seperate for digital part.
Consider amplifiyng thermocouple voltage before switch.
There's a lot of difference between the 40uV/C of a type K thermocouple and a standard 4-20mA loop commercial system. etc for the various other requirements.
Analog muxes can handle the first, though you also have to provide cold junction compensation, but their high and unpredictable resistance make the second more difficult if used on the same input..
etc.
If you want to design a proper product to handle this, you'd better either get learning or employ professionals of some experience.
Are there products of this sort on the market already? - and if not, why not? sounds like a nice idea..... you can't be the first to think of this.....
Maybe because is isn't easy. And probably not possible without some compromises in performance. And much more costly than standard solutions.
And to what gain? Such that a wireman can wire all the different types of sensors randomly, rather than to various specialised inputs? No big deal - tell him to follow the drawing.
Or use eg a MAX6675 shield. What happens if you apply +10v to the input?
Or 20mA?
Or the +48 of a typical 4-20mA loop supply?
Or shunt it with the standard 250 ohm load when measuring 10V?
Or ( given you can do all this with relays etc) what happens if the programmer makes a mistake?