Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Converting 0-10 to 0-20mA
- Thread starter Morcego
- Start date
Short of an actual device to do that you have not provided enough information to pull this off.
A 500 ohm resistor used with 10V equals 20mA but doesn't take into account what you are driving. What it's compliance voltage is, etc.
It is much simpler to convert 0-20mA to 0-10V than what you want.
Keith Cress
Flamin Systems, Inc.-
A 500 ohm resistor used with 10V equals 20mA but doesn't take into account what you are driving. What it's compliance voltage is, etc.
It is much simpler to convert 0-20mA to 0-10V than what you want.
Keith Cress
Flamin Systems, Inc.-
Skogsgurra
Electrical
These guys can help you. They have a very broad spectrum of signal converters.
Quote: "Inputs accepted from most electrical sources, e.g. d.c. mV, V, mA, thermocouples, RTDs, resistance, potentiometers, strain gauges, frequency, a.c. voltage, a.c. current.
Outputs – the common d.c. mA, V ranges, and volt-free relay contacts are available"
Gunnar Englund
Quote: "Inputs accepted from most electrical sources, e.g. d.c. mV, V, mA, thermocouples, RTDs, resistance, potentiometers, strain gauges, frequency, a.c. voltage, a.c. current.
Outputs – the common d.c. mA, V ranges, and volt-free relay contacts are available"
Gunnar Englund
- Moderator
- #5
If your total loop resistance is 500 ohms it will probably work, but I prefer to use the proper matching of signals. Many devices can be configured to output either voltage or current, and many devices can be configured to accept either voltage or current. If you do go to current there are some advantages to 4-20ma over 0-20ma.
My first choice would be to check if the existing equipment can be reconfigured.
My second choice would be skogsgurra's suggestion.
My third choice would be a resistor to bring the total loop resistance to 500 ohms.
To say that the resistor nis the third choice is not to belittle it. There are circumstances where I would happily use the resistor.
respectfully
My first choice would be to check if the existing equipment can be reconfigured.
My second choice would be skogsgurra's suggestion.
My third choice would be a resistor to bring the total loop resistance to 500 ohms.
To say that the resistor nis the third choice is not to belittle it. There are circumstances where I would happily use the resistor.
respectfully
Skogsgurra
Electrical
There is a problem with the 500 ohms approach. Not many 10 V signal sources have the ability to output the required 20 mA. Many 10 V signals are limited to 2 or 5 mA.
Gunnar Englund
Gunnar Englund
- Moderator
- #7
- Thread starter
- #8
Thanks guys for your help,
Wath I need is a driver. I want to use a microcontroller and a A/D converter to generate the output voltage. No problems here. My costumer wants also 0-20 mA output. I has thinking in use the voltage of the D/A to generate the current. The costumer wants a standard current loop device from 0-20mA.
Thanks
Wath I need is a driver. I want to use a microcontroller and a A/D converter to generate the output voltage. No problems here. My costumer wants also 0-20 mA output. I has thinking in use the voltage of the D/A to generate the current. The costumer wants a standard current loop device from 0-20mA.
Thanks
Skogsgurra
Electrical
OK. Then you need a current source. That is essentially an opamp with an emitter follower and a current feed-back. Many diagrams available if you do not to develop from scratch.
There is a collection of design ideas on this address:
You may need to think about galvanic isolation. Most customers expect that from their current loops.
Gunnar Englund
There is a collection of design ideas on this address:
You may need to think about galvanic isolation. Most customers expect that from their current loops.
Gunnar Englund
Morcego talk your customer into 4-20mA not 0-20mA you will lose a bunch of pain!
Keith Cress
Flamin Systems, Inc.-
Keith Cress
Flamin Systems, Inc.-
fliptronics
Electrical
Brand new user here 
I have designed stuff that probably is very close to what you want.
Assuming that what you have is a microprocessor, and you are already thinking of using a D/A converter (you wrote A/D, but I know you meant D/A), then you should look up the Analog Devices AD420.
It conects to the uP via an SPI interface, and includes internally: A/D converter, reference, voltage regulator, current driver. Handles loop compliance voltages up to 24V. It can be configured for 0-20 mA, 4-20 mA, and 0-24 mA.
Resolution is 16 bits, but that is very hard to achieve in any normal noisy digital environment. 12 bits is not too hard.
It can also do voltage output, or just stick a precision resistor in the loop.
Have fun.
Philip Freidin
I have designed stuff that probably is very close to what you want.
Assuming that what you have is a microprocessor, and you are already thinking of using a D/A converter (you wrote A/D, but I know you meant D/A), then you should look up the Analog Devices AD420.
It conects to the uP via an SPI interface, and includes internally: A/D converter, reference, voltage regulator, current driver. Handles loop compliance voltages up to 24V. It can be configured for 0-20 mA, 4-20 mA, and 0-24 mA.
Resolution is 16 bits, but that is very hard to achieve in any normal noisy digital environment. 12 bits is not too hard.
It can also do voltage output, or just stick a precision resistor in the loop.
Have fun.
Philip Freidin
- Status