I need to design a universal analog input module .I have referred to CN-0209.But I could not understand the purpose of ADG442 used in the circuit.Can I get help?
For quick reference, here is a link to the circuit note: http://www.analog.com/cn0209
In CN0209, the purpose of ADG442 is to allow for high precision thermocouple measurements.
One other thing to mention is that in thermocouple mode there is a 2.25V bias voltage generated for the thermcouple by the AD8617 in the circuit,
Another universal input reference circuit that may interest you is CN0325: www.analog.com/cn0325. This is a single channel universal input solution, and allows for a fully configurable input with 4 terminal blocks (like CN0209), or a lower cost option using 6 terminal blocks.
Thanks for the quick response.I need help regarding the following:
That was a very helpful piece of information.Thanks.
The front end will only sample one channel at a time. The procedure would be as follows:
If both channels were thermocouple, the procedure would be similar, though you'd be using he ADG442 switches instead.
If Channel1 was ±10V and Channel2 a thermocouple, then it would be possible to leave Channel 1 connected to the AD8676 and Channel2 connected directly to the AD7193. Then use the AD7193's internal Mux to switch between them.
To support 4-channels there are two options: