How to Read Ac Tester Correct Reading
If you live in the world of HVAC design/installation, sooner or later you're going to need to accept measurements on a circuit using a voltmeter (even if it'south "not your job," we all know how that goes).
So we idea it would be a good thought to put together some basic instructions on using a voltmeter. Even if you've been using a voltmeter for years, there might be some tidbit of data here that y'all hadn't thought virtually before. 🙂
Voltmeter or Multimeter?
These days you'd be hard pressed to find a test meter that merely measured Volts and null else. Everyone articles multimeters which measure volts, current, resistance, and perchance other things too (frequency, capacitance, temperature with accessory probe, etc.). Simply today nosotros're just going to concentrate on making voltage measurements with our multimeter.
Plug the Meter Leads Into the Correct Meter Jacks
This seems obvious, but this author has failed to do this many times. Shown below is a typical multimeter face up layout. This is an actual meter Kele uses in preparation classes. Information technology'due south a few years old but the functionality of the controls is the same as a modern multimeter. Note that your multimeter controls may be bundled somewhat differently or completely differently. No one likes to do it, just y'all might want to actually read your multimeter instruction manual if it hasn't been thrown away/lost by now!
To read voltage, plug the black meter lead into the COM jack and plug the scarlet meter atomic number 82 into the 5/ohm jack.
Do non mistakenly leave the red meter probe in the mA or Amps jack and endeavor to measure voltages between 2 points in a circuit. In the mA or Amps mode the meter leads essentially look like a straight connexion and you volition be shorting out the two measurement points in the excursion. Bad things can happen. Since nosotros are discussing voltage measurements today, that's all we're going to say on the subject. You have been warned.
Gear up the Meter Selector to Volts
The meter selector switch has different major areas for choosing whether you want to read voltage, current, resistance (ohms), or possibly other things. You need to move the selector switch to i of the positions in the Volts surface area (upper correct area on our instance meter).
Set Meter Range (Unless You Have an Machine-Ranging Meter)
Our instance meter has different voltage ranges to choose from based on the maximum voltage y'all await to measure. Ever choose the smallest range that's higher than the highest voltage you are expecting to measure. For example, if you are going to measure 24V then on our meter you would select the 200V range (because the 24V we want to cheque is higher than the next lower range which is 20V).
If you accidentally select a lower range than the voltage you are trying to measure out, the meter won't be damaged, you'll get some kind of "overrange" indication on the brandish. This tin vary from meter to meter. Sometimes it'south a row of horizontal dashes, sometimes it's "OL" for overload, or maybe something completely different.
The only manner you lot should impairment your voltmeter from overvoltage would be if you exceeded the maximum rating for the meter. That value should be in the didactics manual and information technology's almost ever printed on the meter confront too. It'south pretty high, typically something like 750V or 1000V, values y'all volition probably never encounter in HVAC work.
If your meter has an Auto-Ranging function you don't accept to worry well-nigh setting the range, the meter will figure it out for yous. It normally starts on the virtually sensitive range and, if information technology sees an over-range status, moves to the next higher range etc. until information technology finds the about sensitive range that does not result in an over-range condition.
Auto-Ranging is very handy. The downward side is that it can take the meter longer to display a concluding stable voltage reading considering it has to trail-and-error each time to detect the right range. A fixed-range meter manually set to the correct range will stabilize to a usable reading faster since information technology doesn't have to experiment to find the correct range.
Prepare Meter for AC or DC Volts As Needed
If you set the meter to read DC volts and put the probes on a AC voltage source, the meter volition read essentially zero volts (the readout might jump around the zero reading a bit).
If you set the meter to read AC volts and put the probes on a DC voltage source, the meter display will bound up momentarily then "coast" back downward to substantially zero volts over time.
And then be careful – an incorrectly gear up meter will make you think there is no voltage nowadays when there really is.
If you are probing a "mystery circuit" and you're not certain whether the voltage betwixt two points is Ac or DC, yous can endeavour both settings on the meter to run across which gives you a non-zero value.
Place the Meter Probes on the Circuit Points To Be Measured
To make a voltage measurement, you do non need to disconnect annihilation in the circuit. You practise that for current or resistance measurements (which nosotros are not roofing today).
Remember to proceed your fingers on the insulated probe handles, don't affect the metal probe tips with your fingers. You might know the voltage is supposed to be depression (24V) only why have a adventure in example you lot're mistaken or there'due south a brusk in the wiring?
In the example of AC voltage there is no polarity to worry most, the signal will ever read positive on the brandish no matter which way the probes are placed.
In the case of DC voltage, the red probe should continue the more than positive point and the black probe should continue the more negative point. Merely if yous should get it backwards no damage is done, the meter volition but brandish a negative voltage value, the magnitude of the reading will all the same be right and you lot will know that the signal with the black probe is actually the more positive point.
If the brandish shows an over-range condition, just move the meter voltage selector to the next higher range and try again.
Average-Reading Versus True-RMS AC voltmeters
Not all voltmeters are created equal when it comes to measuring AC volts. At that place are ii different measurement techniques in use.
"Average-Reading" Air-conditioning voltmeters only give a right reading if the AC voltage is a sine moving ridge. Nearly AC voltage signals nosotros read in the HVAC world are sine waves (or very shut) and then this is typically acceptable. Less expensive meters tend to use the average-reading measurement technique.
"Truthful-RMS" AC voltmeters will requite a correct reading no thing what wave shape (does not have to be a sine moving ridge). This technique is typically reserved for the more expensive meters.
Do Newbie Exercise On Low Voltages
If yous're new to taking voltage measurements with a voltmeter, nosotros recommend you outset with a low-voltage source only to go on things really safe. A step-down transformer with a 24VAC secondary or a bench ability supply with a depression voltage DC output would be cracking.
Follow the recommendations to a higher place and taking voltage measurements with a multimeter should be second nature in no time at all!
Source: https://www.kele.com/content/blog/2016/03/14/using-a-multimeter-series-voltmeter-basics
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