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Multimeter help
- Thread starter chambersc
- Start date
larrymoencurly
[H]ard|Gawd
- Joined
- Jul 18, 2002
- Messages
- 1,635
Googling or Yahooing for "How to use a digital multimeter" returns several hits.
You could download a manual for a Fluke meter from www.fluke.com. There are differences, but the basics are the same for all meters.
Here is National Instruments' mulitimeter tutorial.
The most important thing is to have the meter leads plugged into the right sockets. Plug the black lead into COMmon, the red lead into Volt/Omega/Diode for almost everything else, including voltage, ohms, and diode check. It's important to NOT plug the red lead into mA (milliAmps) or A (Amps), except when you want to measure current, because that creates virtually a direct short between the meter leads.
The switch settings:
DCV: measure DC volts, such to test batteries and PC power supplies. Red meter lead plugged into V/omega/diode. Black meter lead usually touches ground (typically bare metal on the chassis or connect to a black wire), red lead touches the voltage you want to measure. For example, to measure a PC power supply you'd touch the black meter lead to the plug on a black wire on one of the connectors, while the red meter lead would go to red wire to check the +5.0V rail, to a yellow wire for the +12.0V, an orange wire for the +3.3V, or the purple wire for the +5.0V standby voltage.
ACV: measure AC volts, such as outputs of transformers and wall outlets. CAUTION: be very careful when measuring wall outlets because high voltage can kill you. If you want to practice measuring AC, measure one of those low-voltage transformers that plugs into the wall outlet (but many put out DC instead of AC). Red meter lead plugged into V/omega/diode. The meter leads are connected across the device, but the polarity doesn't matter.
Omega: measure ohms, such as to check fuses to see if they're blown, check wiring for broken connections, or do a rough test of capacitors. Be sure that the power is off before measuring ohms, and before measuring capacitors, discharge them through a 10,000 ohm, 10W resistor first for a minute. Red meter lead plugged into V/omega/diode. The meter leads are connected across the device, but the polarity usually doesn't matter.
Diode Check: (diode symbol >| ))check diodes to see if they're working or not. Diode should measure like an open circuit when meter leads are connected across it one way, should measure almost like a short when the leads are connected the opposite way. Digital meters include a diode check function because their ohms function doesn't work well with diodes. Red meter lead connected to V/omega/diode. The meter leads are connected across the device, and the polarity matters.
DCmA: measure DC milliamps, such as to see how much current is being drained from a battery. Unlike other measurements, which are done with the meter leads connected across the device, to measure milliamps or amps you have to break the connection and splice the meter in series with that connection. If the current is too high, the fuse in the meter will blow or, if there's no fuse, the meter may be damaged. Red meter lead connected to mA.
You want to choose the lowest scale for the most accurate reading, but when in doubt, start off with the highest scale so that the meter reading doesn't overflow. For example, to read a PC power supply, you probably want to use the "20" scale" because the voltages are from 3.3-12V. If you use the 200mV or 2V scale the meter will overflow, while the 200 and 600 scales won't give as much precision.
Be careful not to let your meter leads slip and possibly cause a short. Surfaces can be oxidized and read zero volts unless you scratch them with the meter lead tip.
You could download a manual for a Fluke meter from www.fluke.com. There are differences, but the basics are the same for all meters.
Here is National Instruments' mulitimeter tutorial.
The most important thing is to have the meter leads plugged into the right sockets. Plug the black lead into COMmon, the red lead into Volt/Omega/Diode for almost everything else, including voltage, ohms, and diode check. It's important to NOT plug the red lead into mA (milliAmps) or A (Amps), except when you want to measure current, because that creates virtually a direct short between the meter leads.
The switch settings:
DCV: measure DC volts, such to test batteries and PC power supplies. Red meter lead plugged into V/omega/diode. Black meter lead usually touches ground (typically bare metal on the chassis or connect to a black wire), red lead touches the voltage you want to measure. For example, to measure a PC power supply you'd touch the black meter lead to the plug on a black wire on one of the connectors, while the red meter lead would go to red wire to check the +5.0V rail, to a yellow wire for the +12.0V, an orange wire for the +3.3V, or the purple wire for the +5.0V standby voltage.
ACV: measure AC volts, such as outputs of transformers and wall outlets. CAUTION: be very careful when measuring wall outlets because high voltage can kill you. If you want to practice measuring AC, measure one of those low-voltage transformers that plugs into the wall outlet (but many put out DC instead of AC). Red meter lead plugged into V/omega/diode. The meter leads are connected across the device, but the polarity doesn't matter.
Omega: measure ohms, such as to check fuses to see if they're blown, check wiring for broken connections, or do a rough test of capacitors. Be sure that the power is off before measuring ohms, and before measuring capacitors, discharge them through a 10,000 ohm, 10W resistor first for a minute. Red meter lead plugged into V/omega/diode. The meter leads are connected across the device, but the polarity usually doesn't matter.
Diode Check: (diode symbol >| ))check diodes to see if they're working or not. Diode should measure like an open circuit when meter leads are connected across it one way, should measure almost like a short when the leads are connected the opposite way. Digital meters include a diode check function because their ohms function doesn't work well with diodes. Red meter lead connected to V/omega/diode. The meter leads are connected across the device, and the polarity matters.
DCmA: measure DC milliamps, such as to see how much current is being drained from a battery. Unlike other measurements, which are done with the meter leads connected across the device, to measure milliamps or amps you have to break the connection and splice the meter in series with that connection. If the current is too high, the fuse in the meter will blow or, if there's no fuse, the meter may be damaged. Red meter lead connected to mA.
You want to choose the lowest scale for the most accurate reading, but when in doubt, start off with the highest scale so that the meter reading doesn't overflow. For example, to read a PC power supply, you probably want to use the "20" scale" because the voltages are from 3.3-12V. If you use the 200mV or 2V scale the meter will overflow, while the 200 and 600 scales won't give as much precision.
Be careful not to let your meter leads slip and possibly cause a short. Surfaces can be oxidized and read zero volts unless you scratch them with the meter lead tip.
From Extreme Overclocking, here's another tutorial on measuring PSU rails:http://forums.extremeoverclocking.com/showthread.php?t=137886
Be very careful, methodical and exacting. Hardware's expensive nowadays.
Be very careful, methodical and exacting. Hardware's expensive nowadays.
natermeister
Limp Gawd
- Joined
- Dec 26, 2005
- Messages
- 463
Make sure to get some backprobe pins.
Backprobe pins are basically glorified paper clips that slip between the connector and wire so you can get an accurate reading at the point where the wire and connector meet. You should be able to get them en masse at any electrical warehouse or even auto repair store(NAPA is probably your best bet). Be very careful though. I'm not sure if there are some lines you shouldn't backprobe on a PC powersupply, but find out before trying. In the auto world there are certain electrical connections in cars that must not be backprobed, such as some in the airbag system. Doing so can set off the bag. Like I said, make sure first and be careful.
Backprobe pins are basically glorified paper clips that slip between the connector and wire so you can get an accurate reading at the point where the wire and connector meet. You should be able to get them en masse at any electrical warehouse or even auto repair store(NAPA is probably your best bet). Be very careful though. I'm not sure if there are some lines you shouldn't backprobe on a PC powersupply, but find out before trying. In the auto world there are certain electrical connections in cars that must not be backprobed, such as some in the airbag system. Doing so can set off the bag. Like I said, make sure first and be careful.