Hi,

I am very new to electrical controls and am having difficulty with a problem. Any help would be much appreciated.

I have a 10mA transistor output. I need to provide input to a Data Acquisition Unit (DA100) requires 5VDC input and also provide an input to some counter displays (from what i can tell). With only 10mA transistor output from a frequency to current converter, how can i drive both.

I know this information may be a bit vague but i have very limited knowledge and the data sheets and manuals are confusing me further.

Thanks in advance.

 

10 Ma should be great plenty for several compatible inputs. But knowing they are compatible will require more information. And where the output is coming from would help as well.

Regards,
cww

 

Ohms law says current through a resistor creates a voltage drop.

R = E/I
R = 5V/0.010A
R = 500 ohms

Put a 500 ohm resistor across the input of the Data Acquisition unit, drive your current through the resistor and the DA100 analog input will 'see' 5Vdc at 10mA.

You might be able to run the 10mA current in series with the other devices, if they can be ranged for 10mA.

 

Thank you.

I don't think i have described this very well. I need to use a 10mA output that i have already as the counters and DAC require different voltages.

I have the 5VDC power for the DAC already.

Could i use an opto-isolator circuit to drive both. I am trying to workout the resistances required to get the right drop on the isolator.

Would i need to know the resistance of the DAC as part of the circuit?

Thanks again

 

You are not doing any better at describing what you want. You say that the 10ma. output needs to drive a data acquisition input. That implies that the 10ma. output is a current loop signal that you want to convert to a voltage. But then you say that this 10mA output also has to drive counters. Counters count pulses. They don't directly evaluate analog signals. So it is hard to see the connection between a 10mA analog signal and a counter.

Also you talk about an opto-isolator. These devices are usually used to isolate digital signals, not analog signals. Although analog optical isolators do exist, they are not common.

If all you need to do is work out the resistance to convert 10mA to 5v, that has been well-covered by others in this thread. And no, you don't need to take into account the resistance (by which I assume you mean the input resistance) of the data acquisition system. These systems are usually very high-impedance, and their input resistance would not seriously degrade the effectiveness of a current-to-voltage resistor (if indeed the 10mA output is really a current loop output, which is not at all clear from what you have said).

Robert Scott
Real-Time Specialties
Embedded Systems Consulting
Ypsilanti, Michigan