It doesn't get any simpler than this. But somebody asked, so here we go!
So you have an experimental device to test (DUT). It is supposed to be supplied a voltage to turn it on (lets say: 12V). The first thing you should ask is: How much current can this draw before it blows up?
Once you know the maximum current specification (ex: 200mA), How do you ensure that it doesn't go beyond this maximum value?
Procedure to deliver 12V and a maximum of 200 mA from a DC Power Supply:
What if you cannot find a Current Meter that can handle your required current?
Say you want to deliver 10 A instead. You can still monitor the current by using a Volt-Meter and Sense resistor instead.
Choose a small resistance value for the sense resistor: 1/2 ohm. Since you expect to now deliver 10 A, the resistor must be able to handle the higher power: P=VI = 50 W... not your typical resistor found in a test kit!
Use a Voltage Meter to measure the the voltage across the sense resistor and convert voltage to current: I=V/R. Set your current limit on the PS as before.
Notes:
So you have an experimental device to test (DUT). It is supposed to be supplied a voltage to turn it on (lets say: 12V). The first thing you should ask is: How much current can this draw before it blows up?
Once you know the maximum current specification (ex: 200mA), How do you ensure that it doesn't go beyond this maximum value?
Procedure to deliver 12V and a maximum of 200 mA from a DC Power Supply:
- Find a Current Meter that can handle >200mA.
- Find a DC Power supply that can supply 12V.
- Place the Current Meter in series with the Power Supply (see above photo).
- Most DC power supplies have at least 2 knobs. One labeled "voltage", and the other labeled "current". Set your voltage on the power supply (PS) to 12V.
- Now set your current by:
- turning your PS current knob all the way down to zero.
- replace the DUT with a short by connecting the supply-leads together.
- observe the current-reading on the multimeter and slowly turn the PS current-knob until it reads 200mA (voltage on your PS should read 0 V since leads are shorted together)
- Disconnect the leads and ensure that PS voltage goes back to 12 V.
- Re-connect your DUT and you can now monitor current via the Current Meter.
What if you cannot find a Current Meter that can handle your required current?
Say you want to deliver 10 A instead. You can still monitor the current by using a Volt-Meter and Sense resistor instead.
Choose a small resistance value for the sense resistor: 1/2 ohm. Since you expect to now deliver 10 A, the resistor must be able to handle the higher power: P=VI = 50 W... not your typical resistor found in a test kit!
Use a Voltage Meter to measure the the voltage across the sense resistor and convert voltage to current: I=V/R. Set your current limit on the PS as before.
Notes:
- Keithley makes an all-in-one unit that supplies a voltage and measures current (or vice verse).
- Most Current Meters also function as Voltage Meters and are called "Multi-Meters".
- Its always smart to check the voltage at your DUT to ensure their isn't a voltage-drop over long supply-wires.
No comments:
Post a Comment