- #1
smuscat
- 31
- 0
I need please ideas how to use DAC to measure current.Currently I have built DAC to measure voltage, the type i built is the STAIRSTEP RAMP the 8 bit one.
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Discussion Overview
The discussion revolves around methods to use an Analog-to-Digital Converter (ADC) to measure current, particularly focusing on the conversion of current to voltage for measurement purposes. The context includes practical applications and considerations for both direct current (DC) and alternating current (AC).
Discussion Character
- Technical explanation
- Experimental/applied
- Debate/contested
Main Points Raised
- One participant seeks ideas on using a Digital-to-Analog Converter (DAC) for measuring current, indicating a misunderstanding of the roles of DAC and ADC.
- Another participant explains that an ADC measures voltage and suggests converting current to voltage using a small resistor in series, referencing Ohm's law for calculations.
- A participant mentions the use of current shunts, which are common in industry, and provides a link to a supplier for pre-calibrated shunts.
- One participant expresses concern about the resolution of their measurement setup, noting that the voltage generated by the shunt may be too small for accurate readings.
- Another participant suggests that an amplifier may be necessary to increase the voltage before it reaches the ADC, while also cautioning about the trade-offs of using a larger shunt resistance.
- A later reply acknowledges the suitability of a non-inverting amplifier for the circuit in question.
Areas of Agreement / Disagreement
Participants generally agree on the need to convert current to voltage for measurement with an ADC and the use of shunt resistors. However, there are differing opinions on the specifics of implementation, such as the choice of shunt resistance and the necessity of amplification, indicating that the discussion remains unresolved.
Contextual Notes
Limitations include the potential for confusion between DAC and ADC roles, the impact of shunt resistance on circuit performance, and the resolution constraints of the measurement system.
- #2
mgb_phys
Science Advisor
Homework Helper
- 7,906
- 15
An ADC measures an analogue voltage a DAC generates one.
Since it measures voltage you have to convert the current into a voltage.
The normal way to do this, eg in a digital multimeter - is to connect a small resistor in series and measure the voltage across the resistor, then use ohm's law to calculate the current. With AC it's a little more complicated - you will have to measure the voltage at many points in the AC cycle and calculate the RMS.
What sort of current / voltage are you looking at?
If you are doing this with very high currents (eg car battery) or high voltages (eg household wiring) you probably want to learn a little more before you try.
Since it measures voltage you have to convert the current into a voltage.
The normal way to do this, eg in a digital multimeter - is to connect a small resistor in series and measure the voltage across the resistor, then use ohm's law to calculate the current. With AC it's a little more complicated - you will have to measure the voltage at many points in the AC cycle and calculate the RMS.
What sort of current / voltage are you looking at?
If you are doing this with very high currents (eg car battery) or high voltages (eg household wiring) you probably want to learn a little more before you try.
- #3
Topher925
- 1,563
- 7
These are known as current shunts and are used everywhere in industry. You can buy them for less than $50 from a lot of industrial suppliers and they usually come pre-calibrated. Most shunts available are 50/50 shunts which basically means 50 amps = 50 millivolts so all you have to do is just shift your decimal point.
http://www.rc-electronics-usa.com/current-shunt.html
- #4
smuscat
- 31
- 0
DC current i need to measure.I have a problem because it reads a resolution of 5V/256 0.02Volts the voltage is too large i think.Beause the voltage generated by the shunt is too small i think.
- #5
mgb_phys
Science Advisor
Homework Helper
- 7,906
- 15
For a real world application you will need an amplifier before the ADC.
In order to get a larger voltage, you would need a larger shunt resistance which will waste energy and reduce the voltage in the circuit.
For somethign like a simple science fair experiment or just to roughly monitor a voltage in a low current application you could use a large eg 1 Ohm resistor.
In order to get a larger voltage, you would need a larger shunt resistance which will waste energy and reduce the voltage in the circuit.
For somethign like a simple science fair experiment or just to roughly monitor a voltage in a low current application you could use a large eg 1 Ohm resistor.
- #6
smuscat
- 31
- 0
Thanks an amplifier like a non inverting one fits well in my circuit.
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