Can I get an application note on "ISOLATED 4-20ma LOOP POWERED Thermocouple/RTD Transmitter".
We do not have an App note for an isolated loop-powered temperature transmitter, but we do have some other material that you may be interested in:
CN0267: Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface
CN0145: 4 mA-to-20 mA Loop-Powered Temperature Monitor Using the ADuC7060/ADuC7061 Precision Analog Microcontroller
CN0300: Complete Closed-Loop Precision Analog Microcontroller Thermocouple Measurement System with 4 mA to 20 mA Output
CN0206: Complete Type T Thermocouple Measurement System with Cold Junction Compensation
CN0289: Flexible, 4 mA-to-20 mA, Loop-Powered Pressure Sensor Transmitter with Voltage or Current Drive
I will go through these.
What is the time frame for your application? I am in the isolation group and am putting together an application note for later this year. If you want to discuss your isolation options off line I will be happy to help.
After your 26th june communication I have been going through various options to make an ISOLATED UNIVERSAL LOOP POWERED 4/20ma Converter.
Everything stops at a place –THE ISOLATED DC-DC converter from say AD693 ‘S REFERENCE VOLTAGE OUTPUT to an isolated 3.3v say 5ma.
Some DAC ‘s like Ti’s dac161P997 could be another option with a micr sitting on an 3.3v@5ma isolated DC-DC Converter.
Hence may I know if there could be such a low power 3.3 V,5MA, ISOLATED DC DC Converer of 2kv IAOLATION POSSIBLE
The DC/DC converter is difficult. If you are running an interface on loop power, I assume you will have a power budget of 3 mA, and need to get that power across the isolation to a sensor and ADC combination. So you need a converter that is high efficiency at low power. If you have a fixed load, this can be done with a home made single purpose supply. Once you add in variable loads, tight regulation, small size and isolation, basically a general purpose DC/DC the efficiency at light loads gets bad, due to the overhead of the regulation and control. Most DC/DC modules draw a lot of power just sitting idle. Actually our ADuM5010 is better than most with about 5mA of quiescent current, but the efficiency is low, and when you draw your 3mA from the output, you need about 14mA from the input. Not really compatible with loop power.
I think a supply that would meet your needs is possible, but not on the roadmap right now. I don't know of any off the shelf solutions that would meet your needs. This is good feedback for planning purposes, thank you for your input. Please let me know if I have misunderstood your requirements.
Thanks for putting across all the issues related to this problem with an excellent clarity.
May I know what you meant by “If you have a fixed load, this can be done with a home made single purpose supply”. Can I get some more information on this.
I am sure that you are aware of such a product as indicated by me ARE AVAILABLE IN THE MARKET WITH PC programmability.
May be, I could request you to air your thoughts on possible directions that one may work to achieve this solution.
If the load is fixed, and temperature is fairly well controlled, then there is no regulation or feedback required, so a power supply can be as simple as a 555 timer a transformer a diode and a cap. These can actually be fairly efficient. and can work at very low power with low quiescent current.
If you have a supply that can work under your conditions I would like to review its data sheet.
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