Chinese electronics products tested (163 tests): Aneng AN302 autoranging multimeter tested

(Published on 23/01/2019)

For just over ten euros you can buy this ultra flat autoranging true RMS multimeter. It can measure just about anything except currents. How good is such a cheap meter? We tested all measurement functions and were quite satisfied.

Introduction to the AN302

Many functions for little money
Chinese Aneng is known for bringing multimeters with many options to the market for very little money. This is also the case with the AN302. It measures direct voltages, alternating voltages, resistors, capacitors, frequencies and diodes. The only thing this meter can't measure are currents, but that's just that option you rarely use in practice. Remarkable is that the meter is capable of measuring the true RMS of an AC voltage. This is the value of the AC voltage that generates as much thermal power in a resistor as a DC voltage of the same value. This is useful, for example, if you need to calculate the power that a light dimmer voltage generates. The maximum number of counts is 8,000, another specification that is not obvious for a ten euro meter. Even more useful functions are the HOLD and REL and of course the autoranging. Finally, the AN302 also has an NCV mode, which stands for 'Non Contact Voltage'. This allows you to contactlessly detect the electromagnetic fields of alternating voltages, useful for locating power cables in the wall.

What you get
For your ten euros you not only get the meter itself with two test leads, but also a handy carrying bag, a carrying strap and a manual in excellent English.

The AN302 multimeter
The meter itself is only 11.5 cm x 5.5 cm x 1.2 cm in size. Because of the very flat design there is of course no room for normal 4 mm jacks. The two test leads with a length of 70 cm are attached to the housing, which saves some money but for some applications is awkward. On the front are six push buttons, on the back is a buzzer and a white LED that you can turn on when you push the HOLD push button longer than two seconds.

The function of the six buttons

ON/OFF
The round, red button is the on/off switch. The AN302 also has an automatic power-off function. After fifteen minutes without any button push, the meter switches itself off. Just before that you will be warned by a number of beeps. If you want to deactivate this function, press the HOLD button first and then also the ON/OFF button.
FUNC.
The meter has two function groups and this button switches between these groups. Group 1 measures DC and AC voltages in the V-range and also switches on the Non Contact Voltage detector. Group 2 measures DC and AC voltages in the mV-range, resistors, capacitors, frequencies and diodes.
SELECT
Selects the measurement function in the group you have chosen. The selected function is identified by the function symbols that light up in the display.
REL
Enables the relative measurement function. In this function, the current measured value is stored as a zero reference in the memory and the display goes to zero. All new measurements are referenced to this value. The stored value is subtracted from the measurement. However, this option does not work in all measurement functions.
RANGE
After pushing this button once, the AN302 exits autorange mode and you can then manually set the measuring range by pushing this button several times. Each button push increases the measuring range by a factor of ten. After reaching the highest measuring range, the next button push selects the lowest measuring range again.
HOLD
After a short push of this button, the current measured value is frozen on the display. After a second push, the measurement starts again. Push this button for more than two seconds to activate the white LED in the back of the case. Push again for more than two seconds to switch this LED off.

Powering the AN302
This meter is powered by a button cell of the type CR-2032. This 3.0 V voltage source is not included. The first thing you have to do is mount such a cell in the meter. The AN302 has no battery compartment, you have to remove the back of the housing by unscrewing three small screws. In a cut-out in the PCB you can then mount the CR-2032. Not very handy, but of course much cheaper in production than a housing with a battery compartment.
The mechanical construction of the meter looks a bit rickety. The three screws are small and the question is how often you can replace the button cell before these screws no longer hold and the housing no longer closes. Proper closing of the housing is absolutely necessary to press the button cell firmly on its contacts and to put the buzzer in good contact with two small contact springs on the PCB.

The electronics in the AN302
In the picture below we present the front and back of the PCB. Except for a few parts, all passive components are miniature SMDs. Remarkable are two series-connected larger resistors of 5 MΩ, which are in the input circuit and set the input resistance of the meter to 10 MΩ. Next to the microprocessor, which is hidden under a blob of paste, is a P24C02A EEPROM. The microcontroller is controlled from a 4 MHz crystal. Below the two 5 MΩ resistors is a protection circuit, composed of two transistors and a PTC. Four of the six push buttons are 'switched' by conductive rubber mats, which you push on the contact strips on the PCB. The ON/OFF and FUNC. push buttons are actually designed as 'real' push buttons that contain three contacts. In order to make the meter as thin as possible, the push buttons are half-immersed in a hole in the PCB. When you push the button, a considerable force is applied to the six minuscule solder islands on the PCB. The risk that such a switch will ever tear out of the PCB is therefore not unimaginable.

The specifications of the AN302
The manufacturer provides the following specifications:
- Display range: 8000 units
- Number of measurements: three per second
- DC voltage measuring ranges: 80.00 mV ~ 800.0 mV ~ 8.000 V ~ 80.00 V~ 600.0 V
- Accuracy DC voltage measurement: ±(0.5 % + 3 digits)
- AC voltage measuring ranges: 80.00 mV ~ 800.0 mV ~ 8.000 V ~ 80.00 V~ 600.0 V
- Accuracy AC voltage measurement: ±(1.0 % + 3 digits)
- AC voltage frequency range: 40 Hz ~ 1 kHz
- AC voltage measuring principle: true RMS
- Measuring ranges resistors: 800.0 Ω ~ 8.000 kΩ ~ 80.00 kΩ ~ 800.0 kΩ
- Measuring ranges resistors: 8.000 MΩ ~ 80.00 MΩ
- Accuracy resistor measurement: ±(0.5 % + 3 digits) ~ ±(1.5 % + 3 digits)
- Measuring ranges capacitors: 9.999 nF ~ 99.99 nF ~ 999.9 nF ~ 9.999 μF
- Measuring ranges capacitors: 99.99 μF ~ 999.9 μF ~ 9.999 mF
- Accuracy capacitor measurement: ±(5.0 % + 20 digits)
- Measuring range frequencies: 99.99 Hz ~ 999.9 Hz ~ 9.999 kHz ~ 99.99 kHz
- Measuring range frequencies: 999.9 kHz ~ 2.000 MHz
- Accuracy frequency measurement: ±(0.1 % + 2 digits)

The AN302 on the test bench

The input resistance
At all voltage ranges, the measured input resistance is 10.03 MΩ.

Measuring DC voltages
We measured in the autoranging function and compared it with our laboratory meter VC650BT from Voltcraft. A power supply that can be set to one mV was programmed until round numbers appeared on the display of the AN302 In the table below you can see what our VC650BT thought of it. Without doubt excellent results, in most cases there is only a deviation of a few mV between the two meters.

Measuring 50 Hz AC voltages
We used our function generator as a voltage source and set it to a sine wave of 50 Hz. The results of the AN302 are more than excellent, see table below. Unfortunately we do not (yet) have a variac in our lab, so we can only use the mains voltage or our function generator as a voltage source. Measuring the mains voltage gave a result on the Aneng of 235.1 V and on the Voltcraft of 235.36 V.

Measurement of the frequency range for AC voltages

We have set the output voltage of the function generator to 3.00 V and varied the frequency. As the graph below shows, the frequency range of the AC voltage measurements easily meets the specifications. Between 10 Hz and 2 kHz there is hardly any voltage drop. At higher frequencies, however, the accuracy drops quite quickly.

Accuracy of the RMS calculation
Various algorithms exist to calculate the RMS value of an AC voltage. We were curious to see how this cheap meter that is advertised as 'true RMS' performs in this field. In the table below we have compared the AN302 indication with that of our reference meter for various signal shapes.

Measuring resistors
We have a set of six very accurate resistors with a tolerance of 0.1 %. When the two test leads of the AN302 are short-circuited, it turns out that they have a resistance of 0.5 Ω. Now we can use the handy REL option. Pushing this button once and that resistance is stored as a relative zero value in the memory and is automatically subtracted from all resistance measurements. The accuracy of the measured resistors is (again) excellent, see table below.

The measurement results of six 0.1 % resistors.
(© 2019 Jos Verstraten)

Measurement of capacitors
Our reference consists of a set of eight Vishay MKP capacitors with a tolerance of 1.0%. The measurement results are shown in the table below.

Measurement of frequencies
According to the specifications, the AN302 must measure up to 2,000 MHz. However, it does not specify how high or low the sensitivity for this function is. This can be easily measured with our function generator. Unfortunately, the practical usefulness of this measurement function is negligible. Connected to a sinusoidal input signal with an amplitude of 400 mV and a frequency of 50 Hz, the meter displays the exact frequency. This remains the case up to about 5 kHz. Afterwards the sensitivity starts to decrease rapidly. At 50 kHz a sine wave with an amplitude of 3.9 V was required to get the exact frequency of the signal in the display. At 100 kHz the required amplitude was increased to 13.1 V! The measurements were then repeated with a square wave signal. Even with such an in principle easily measurable signal, at 100 kHz an amplitude of 9.0 V was needed to get a good frequency reproduction in the display.

The Non Contact Voltage function
To activate this function, push the SELECT button three times after turning the meter on. 'EF' appears on the display. If you then bring the AN302 near an AC conductor, the meter will beep and the LED will flash. The closer to the live conductor, the higher the frequency. In addition, the display will show a number of dashes indicating the size of the electromagnetic field. However, this function works too well, the meter is too sensitive. If you try to locate a power line in a wall, the meter will beep in a strip of at least 30 cm around the location of the wire. The exact location of the wire is therefore not easy to detect.

Some other functions

DIODE
In this mode you measure the voltage across a conductive diode. You must connect the red probe to the anode! The measuring current is 1.6 mA.
CONT
In this mode, the meter will beep if the resistance between the pins is less than 50.00 Ω. This function is also ideal for measuring very low resistors. Unfortunately, the REL option does not work in this mode, so you have to subtract the 0.5 Ω of the measuring cables yourself from the measurement result. In the table below, the measured values of five very accurate wire-wound resistors are shown.
LOW BAT
If the button cell voltage drops below 2.4 V, the well-known 'low battery' symbol will appear on the display.

Our opinion about the Aneng AN302

This meter, which costs just over ten euros, meets almost all the requirements for a multimeter in terms of measurement performance. However, you cannot trust the AN302 to measure frequencies. The lack of a current measurement is also a small shortcoming.
We are less enthusiastic about the mechanical construction of the device. The way in which the button cell is clamped into the housing is ingeniously conceived, but not very reliable in the long run. The buttons do not work very well and often you have to press twice to activate a function. Nevertheless, our final opinion is very positive. Aneng has succeeded in bringing a very useful and accurate multimeter on the market at a very low price.

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ANENG AN302 Push-button Digital Multimeter