Difference of true rms tester from simple one. Why Choose True RMS Instruments? Calculating the RMS value
It is not always necessary to carry out measurements only to correctly connect the measuring device. It is very important to answer the question: why am I measuring this? To measure the current when checking the heat release in the wire, one parameter is required, to measure the current to determine the charge level of a capacitor or battery - quite another.
Parameters can be expressed as mean, rms ( RMS, Root Mean Square), instantaneous or peak value. Not only the type of load is important, but also whether we are dealing with alternating or direct current and what the shape of the voltage and current looks like. Closely related to the concepts of voltage and current are power and energy.
Instantaneous values
Instantaneous current, voltage and power are values \u200b\u200bthat correspond to a particular moment in time. Any signal consists of an infinite number of instantaneous values. In the case of voltage, this is written as.
Consider a circuit consisting of a series-connected resistor and inductor connected to a sinusoidal voltage source with peak voltage and frequency Hz.
Sinusoidal voltage as a function of time, in this case, can be written as:
(1)
The current has a maximum value and is shifted in relation to the voltage:
(2)
Power as a function of time is the corresponding instantaneous voltage and current values:
(3)
The figure below shows graphs of voltage, current and power.
For example, the gray line shows instantaneous values \u200b\u200bfor a point in time ms:
v (4.2) \u003d 2.906 V
i (4.2) \u003d 0.538 A
p (4.2) \u003d 1.563 W
At a certain point in time, the instantaneous voltage and current can always be multiplied by calculating the instantaneous power.
Average values
Average values \u200b\u200bare the most commonly used parameters.
If the multimeter is set to measure DC values, the average voltage and current are measured. In addition, if the multimeter is operating in dc measurement mode, it will also measure the average voltage or current for ac signals. In the case of symmetrical AC voltage, the multimeter will show which is the correct value.
Voltage and current
The average is the sum of all products of instantaneous values \u200b\u200bdivided by the number of measurements taken. If measurements are made an infinite number of times, then we can go to the limit, in which the measurement time interval → 0 and the sum will turn into an integral. In general:
(4)
For voltage, we get:
(5)
Multimeter
As mentioned earlier, a multimeter set to DC measurement measures the average voltage or current. In digital instruments, this average is obtained using RC-filter. The input signal is continuously averaged over a time constant. As a formula:
(6)
Voltage averaging by RC filter
Energy and power
Equation (3) shows that the product of instantaneous voltage and current results in instantaneous power. If you add up the instantaneous power multiplied by the infinitesimal time, the result is energy. Because :
(7)
Indeed, energy is power multiplied by time: and energy packets can always be added to calculate the total energy.
As an example, again take the series connection of an inductor and a resistor. In the figure below, the black line shows the dynamics of energy over time, calculated in accordance with equation (7).
The power curve in the case of voltage and current of alternating polarity, also has a periodic amplitude change with double the frequency. Since the energy is dissipated in the resistance, the gray area of \u200b\u200bthe positive values \u200b\u200bof the power curve is larger than the negative area.
The energy value (black line) at any given time is equal to the area under the power curve up to that moment. It is clearly seen that the energy periodically increases more strongly than it decreases as a result of the amplitude asymmetry of the power curve about the axis.
The figure shows the time period. The energy within this time interval that entered the system is indicated and calculated as follows:
(8)
The average power over a certain period of time is equal to the total amount of energy during this time, divided by the measurement time:
(9)
If this is substituted into equation (8), the average power can be calculated for any.
(10)
This equation was obtained in accordance with (4). The active power is always the average power.
This equation for calculating the average power dissipation is always valid because the calculation is based on instantaneous values. It doesn't matter if the current is DC or AC, what the voltage and current waveform looks like, and whether there is a phase shift between voltage and current.
The equation for calculating the average power is at the heart of the method used in power meters. Electricity meters at home and in enterprises operate in accordance with equation (8), which can be rewritten as:
(11)
The upper limit in the integral is the point in time at which the energy meter reads a value.
Effective ( RMS) values
Root mean square ( RMS), or the effective value is the voltage or current value at which the same power dissipates across the load as at constant voltage or current.
With alternating voltage with an effective value 230V the same amount of heat will be generated at the load as at constant voltage 230V... The rms value applies only to heat dissipation in the resistive load. For example, the value RMS current is useful for measuring voltage under load in a wire (\u003d resistive), but not to measure the charging current of a battery or capacitor (\u003d electron flow).
Averagesquare value
RMS is an abbreviation for Root Mean Square, which literally translates to rms value.
Over voltage or current as functions of time to calculate the value RMS three mathematical operations are carried out sequentially: squaring, averaging, and square root extraction. Why is that?
Power dissipated across a resistor connected to a voltage source:
(12)
For instantaneous power and voltage:
(13)
The calculation of the average power as a function of time is shown in (10). we can find from (13):
(14)
Since is a constant, it can be taken out as an integral:
(15)
By moving the voltage in equation (12) to the left side, we can calculate the voltage from the average power and resistance:
(16)
Then, we substitute the calculated average power from (15) into equation (16):
(17)
Reducing the resistance values, we get:
(18)
It is clearly seen that this equation consists of three parts: square, mean and square root.
In the above calculations, the value of the voltage across the resistor was calculated. The same can be done for the current through the resistor:
(19)
Most multimeters cannot calculate the effective value of the measured voltage. To find out the rms value, a special instrument is usually needed.
The figure below shows how the instrument calculates the measured voltage. True RMS(true rms values). True RMS the device, in practice, uses a slightly different method of operation, in which only one multiplier is needed. Analog multipliers must have very low temperature drift and offset, which makes these instruments quite expensive.
Analog circuit for obtaining RMS values
In addition, you can make a calculation RMS programmatically with serial digital values \u200b\u200bof the measured voltages. This approach is commonly used in multimeters and.
Pseudo RMS
Most multimeters do not measure RMS-values \u200b\u200bwhen AC mode is selected. However, they seem to give effective values \u200b\u200bwhen measuring alternating voltages and currents. However, the displayed values \u200b\u200bare only valid when measuring a sinusoidal signal.
A simple instrument first straightens the signal to be measured. Then RC- A low-pass filter highlights the average value, which is scaled so that the meter shows the effective value. As an equation:
(20)
The disadvantage of this approach is that it is only suitable for sinusoidal signals. For any other waveform, an erroneous effective value will be obtained.
Rated power?
Especially in audio technology, the term "rated power" or is widely used. This is a misnomer by definition.
Slightly above, speaking about energy and power, it is shown that the working power is calculated from the total amount of energy divided by the time for which this energy is measured, see equation (9). The total energy is determined by summing all instantaneous energy packets, see equation (11). This is the only correct way to calculate active power.
As indicated above, the effective value is equivalent to a constant voltage or current that will deliver the same power at the same resistance. This indicator is calculated as the square root of the mean of the square of the instantaneous voltage (or current). There is no reason to think that these three mathematical operations have to be done for instantaneous power. It would be meaningless.
Chinese company multimeters Victor Nowadays, you can often find them on the Chinese Internet sites AliExpress, Banggood, and there are quite a few of them at Russian distributors. What are the budget multimeters of this Chinese company? Today we have a multimeter on review Victor VC890D with True RMS function. The word True RMS is mentioned here for a reason, since there is exactly the same Victor VC890D multimeter, but without True RMS, which has a slightly different appearance and characteristics, as well as several ranges for measuring the capacitance of capacitors. This multimeter has only one range: 2000 μF. And they are built on completely different chips.
There is also a model Victor VC890C +, differs only in the ability to measure temperature and the presence of a thermocouple in the kit. Otherwise, absolutely identical devices.
The average cost of a multimeter on AliExpress is around $ 25.
So, the multimeter was ordered on AliExpress, it came without a box, just wrapped in several layers of bubble wrap. You can see the complete set below:
Here we see the multimeter itself, probes, instructions in Chinese, as well as a piece of paper with a control stamp.
Victor VC890D specifications:
- TrueRMS (Arbitrary Waveform Measurement)
- Basic accuracy ± 0.5% (DCV)
- DC voltage measurement up to 1000 V (± 0.5%)
- AC voltage measurement up to 750 V (± 0.8%)
- DC / AC current up to 20A (± 1.5%)
- Resistance measurement up to 20 MΩ (± 0.8%)
- Capacitance measurement up to 2000 μF (± 2.5%)
- Chain ring
- Diode test
- Measuring the gain of transistors
- Functionality: 3 measurements / sec
- Auto-hold
- Auto power off
- LCD display 4 digits with backlight
- Power supply 9 V (crown)
- Dimensions: 186 x 87 x 47mm
- Weight with battery: 364g with cover, 280g without cover
The multimeter has a removable silicone case. There is a stand. There is a holographic sticker at the end, the Victor inscription also shimmers in the light, this is clearly seen in the very first photo.
When the power is turned on, all possible symbols are shown on the display, and the multimeter also emits a short beep. To the right of the Hold button (it also turns on the backlight by a long press) is a red LED. When switching between modes, a beep sounds and a red LED flashes.
The probes are the most common, the measured resistance on a table multimeter is ~ 0.1 Ohm.
The silicone case contains holders for the probes.
There are 4 sockets for probes - 2 standard and 2 sockets for measuring current. The first socket is up to 200 mA, the second is for currents up to 20 A, both with appropriate fuses, accessible through the battery compartment.
What is TrueRMS for?
TrueRMS is "true rms value". Those. TrueRMS refers to the measurement of AC current and voltage values. Nowadays, we are more and more surrounded by household appliances with non-sinusoidal current consumption and introducing distortions: computers, UPS, frequency converters or the same PWM. For example, when measuring the PWM current consumption, the values \u200b\u200bcan be overestimated, and, say, when using a single-phase diode rectifier, they can be underestimated. For example, a situation may arise that you have measured the current consumption of 7A, and your machine is constantly knocked out or a 10A fuse burns out. This is where a multimeter with the function can come in handy TrueRMS, which can determine the real effective value of the alternating current, regardless of its shape.
Measurements
I propose to take measurements and see how accurately and quickly the device works in different modes. You can see the speed of reaction in the video.
Let's start by measuring the resistance of high-precision 0.01% resistors from TDK and Vishay. We will change the probes to a slightly higher quality and lower resistance in order to reduce the influence of their internal resistance. It would be possible with relatives, but still, many radio amateurs later change them to better ones or as a result of rapid wear.
The multimeter gives accurate readings after a while ( the video clearly shows it)... And since when measuring, both hands are busy, and the camera was taking pictures with a release delay, then the resistance values \u200b\u200bin some frames turned out to be not steady. But still, in most cases, the resistance readings are somewhat overestimated, although everything is within the stated measurement error.
Let's check how accurately the multimeter measures DC voltage. To do this, take an ION on the AD588BQ microcircuit, the temperature drift of which does not exceed 1.5 ppm / ° C, with an output voltage of 5V and 10V. More precisely, 5.00031V and 10.00027V (measured with an Agilent 34401A multimeter).
To measure AC voltage, a 12/220 inverter was used, giving out a pure sine wave. As you can see, the readings are pretty accurate.
Measuring the gain of transistors hFE:
The display backlight turns off automatically after about 15 seconds after holding the Hold button for a long time.
In diode measurement mode, the voltage across the open probes is displayed. As you can see, it is about 1.6 Volts (many specifications for this model indicate the wrong voltage 3V). Therefore, they cannot check the LEDs, because more voltage is needed to test them.
Ringing diode 1N4007. The forward voltage drop across the diode is displayed.
As you can see, it is 0.565 Volts.
To measure the capacitance of capacitors in this model, only one range is provided - 2000 μF. The device, depending on the measured capacity, shows the dimension: micro or nano, i.e. essentially automatic range selection. Minimum dimension: 0.001 nF, i.e. 1 pF.
Electrolyte 100 μF.
Root mean square (RMS). Effective or effective value
True Root Mean Square (TRMS)
Root-mean-square (RMS) - mean square value - eng.
True Root-Mean-Square (TRMS) - true root mean square value - eng.
For any periodic function (for example, current or voltage) of the form f \u003d f (t), the rms value of the function is defined as:
then the effective value of a periodic non-sinusoidal function is expressed by the formula
 |
Since Fn is the amplitude of the n-th harmonic, then Fn / √2 is the effective value of the harmonic. Thus, the resulting expression shows that the effective value of the periodic non-sinusoidal function is equal to the square root of the sum of the squares of the effective values \u200b\u200bof the harmonics and the square of the constant component.
For example, if a non-sinusoidal current is expressed by the formula:
 |
then the rms current is:
 |
All the above ratios are used when calculating in ISKZ measuring testers, in UPS current measurement circuits, in network analyzers and in other equipment.
True Root-Mean-Square (TRMS)
Most simple testers cannot accurately measure the RMS value of a non-sinusoidal signal (that is, a signal with large harmonic distortion, such as a square wave). They correctly determine the RMS voltage for sinusoidal signals only. If such a device measures the RMS voltage of a rectangular shape, then the reading will be erroneous. The reason for the error is that conventional testers, when calculating, take into account the fundamental harmonic (for a conventional network - 50 Hz), but do not take into account the higher harmonics of the signal.
To solve this problem, there are special instruments that accurately measure the RMS, taking into account higher harmonics (usually up to 30-50 harmonics). They are marked with TRMS or TRMS (true root-mean-square) symbol - true root mean square value, True RMS, true RMS.
So, for example, a conventional tester can measure with an error the voltage at the UPS output with an approximated sine wave, while the APPA 106 TRUE RMS MULTIMETER tester measures the voltage (RMS) correctly.
Remarks
For a sinusoidal signal, the phase voltage in the network (neutral - phase, phase voltage) is:
USCZ f \u003d Umax f / (√2)
For a sinusoidal signal, the line-to-line voltage (phase-to-phase, interlinear voltage) is:
URMS l \u003d Umax l / (√2)
The relationship between phase and line voltage:
USCZ l \u003d USCZ f * √3
Legend:
f - linear (voltage)
l - phase (voltage)
RMS - rms value
max - maximum or peak value (voltage)
Examples:
Phase voltage 220 V corresponds to line voltage 380 V
Phase voltage 230 V corresponds to line voltage 400 V
Phase voltage 240 V corresponds to line voltage 415 V
Phase voltage:
Mains voltage 220 V (RMS), - voltage peak value about ± 310 V
Mains voltage 230 V (RMS), - voltage peak value about ± 325 V
Mains voltage 240 V (RMS), - voltage peak value about ± 340 V
Line voltage:
Mains voltage 380 V (RMS), - voltage peak value about ± 537 V
Mains voltage 400 V (RMS), - voltage peak value about ± 565 V
Mains voltage 415 V (RMS), - voltage peak value about ± 587 V
Below is a typical example of phase voltages in a 3-phase network:
 |
G.I. Atabekov Fundamentals of the Theory of Chains p. 176, 434 p.
Accurate measurements are a difficult task facing technologists and service specialists of modern production facilities and equipment of various organizations. Our daily life more and more includes personal computers, variable speed drives and other equipment with non-sinusoidal characteristics of current consumption and operating voltage (in the form of short-term pulses, with distortion, etc.). Such equipment can cause inadequate readings on conventional averaging meters (which calculate the rms value).
Why Choose True-RMS Instruments?
When we talk about AC currents, we usually mean the mean effective heat dissipated or the root mean square (RMS) current. This value is equivalent to a DC current that would produce the same thermal effect as the AC measured and is calculated using the following formula:
.
However, when the sinusoidal curve deviates from the ideal shape, this coefficient ceases to work. For this reason, averaging meters often give incorrect results when measuring currents in modern power networks.
Linear and non-linear loads
Figure: 1. Curves of voltage of sinusoidal and distorted form.
Linear loads, which include only resistors, coils and capacitors, are characterized by a sinusoidal current curve, so there are no problems when measuring their parameters. However, in the case of non-linear loads such as variable frequency drives and power supplies for office equipment, distorted curves will occur in the presence of interference from high-power loads.
Figure: 2. Curves of current and voltage of the power supply unit of a personal computer.
Measuring the rms currents from such distorted curves using conventional meters can give a significant underestimation of the true results, depending on the nature of the load:
|
Device class | Load type / curve shape
|
|||
| PWM (meander) | single phase diode rectifier | three-phase diode rectifier |
||
| RMS | correctly | overestimation by 10% | understatement by 40% | underestimation 5% ... 30% |
| True RMS | correctly | correctly | correctly | correctly |
Therefore, users of conventional devices will have a question why, for example, a 14-amp fuse regularly blows, although according to the ammeter the current is only 10 A.
True RMS Instruments (True RMS)
To measure current with distorted curves, it is necessary to check the shape of the sinusoid using a signal curve analyzer, and then use a meter with averaging readings only if the curve turns out to be a truly ideal sinusoid. However, it is much more convenient to use a True RMS meter all the time and always be confident in your measurements. Modern multimeters and current clamps of this class use advanced measurement technology to determine the real rms values \u200b\u200bof AC current, regardless of whether the current curve is a perfect sinusoid or distorted. For this, special converters are used, which determine the main difference in cost with budget counterparts. The only limitation is that the curve must be within the acceptable measuring range of the instrument used.
Everything that concerns the features of measuring non-linear load currents is also true for measuring voltages. Voltage curves are also often not perfect sinusoids, resulting in averaging meters giving incorrect results.
Based on the examples described above, it is recommended to use True RMS devices for measuring currents and voltages in modern high-tech electrical systems.
Two years ago I reviewed this multimeter model. It was a device ordered at the request of my friend. This time I ordered it for my own (I expected it as a gift). I received the order in the spring. But, I think, the review has not lost its relevance. So what made me do this review? In that topic, I made one serious omission. I did not notice the True RMS inscription at all. I also missed some measurements. I will check in more depth.
And it would not hurt to remind you that there is such an inexpensive multimeter (the cheapest with True RMS). After all, not everyone read that review.
I used a discount to buy a multimeter. If you have points, you can use them too.
First, let's take a quick look at how everything arrived. The package is trackless. I really didn't want to pay for the track, knowing especially that everything comes from this store so well (less than 30 days from payment). 
Standard package without a "bubble". Inside, the polyethylene foam was supposed to protect the device from all surprises. 
He did not protect against all surprises. As a result, we have a seriously flattened box. But the device is safe and sound.
Here's what was included:
1-Box
2-Multimeter
3-Instruction in "native" Chinese. The scan can be viewed here:
4-Two AAA batteries (inside the multimeter).
5-Lace on ……. hand? More like two fingers (well, very small).
6-Warranty card. 
During this time, nothing has changed in the design of the device. 
Holographic sticker confirming authenticity (hieroglyphs in the center and its perimeter). 
I open the lid and the device is ready for use. Probes with wires are neatly collected in a special pocket. Length of wires 37cm + probes 10cm. There is very little space. With difficulty, everything fits. 
The wires are thin and not soft. If you throw it in the car and use it occasionally, it's enough for a long time. The probes will soon need to be replaced with daily use. New ones will not fit into the pocket. You will have to drill a hole (hole) on the side. Otherwise, the lid will not close.
I did not notice this inscription then. 
On the cover there are brief characteristics with the capabilities of the device. 
On the store page for more details, indicating the measurement error. 
It's actually much better. More on this later.
The device itself is in a plastic case with a cover that covers the front panel. The body is neatly made, everything fits snugly enough.
Small multimeter. 
Weighed it. With batteries 127g. 
The inscriptions on the device are clearly defined. 
The lid has a latch, closes tightly, you need to make a little effort to open it. There is a slot in the cover. You can only close the device with a lid if the mode switch is set to the correct left “off” position. 
The cover can be used as a stand. Although, such use is questionable. 
The operating mode switch is disk, with a clear fixation and a click.
When turned on, the mode with automatic selection of the measuring range is automatically activated. There is a yellow "RANGE" button for manual range selection, with cyclic switching.
There is no display backlight.
Auto switch off.
If no operations are performed with the device using the rotary switch or buttons, then after 14-15 minutes it will give four short warning beeps (loud enough). After the fifth longer time, the multimeter goes into sleep mode and turns off. To revive it, you will have to turn the mode switch to the OFF position, and then turn it on to the desired position. It does not react to pressing the buttons, it will not be possible to "revive" this way.
Enabling / disabling the "RANGE" automatic measurements mode (yellow button).
Works when measuring AC / DC resistance and voltage. To do this, click on the button. A short press switches the sub-bands. In the mode of measurement of capacity and frequency, the automatic measurement mode is not disabled.
Relative measurements "REL" (blue button).
Works when measuring voltage and resistance.
When measuring frequency, switches to duty cycle measurement mode.
Display resolution: 4000 readings with floating point.
The display capabilities are redundant in relation to the capabilities of the device.
The device is powered by two AAA batteries. This is undoubtedly a plus. 
Batteries were included. Ordinary salt, it is better to change them. If they flow, the springs will spoil.
Who cares, let's take a look what's inside.
I unscrewed one self-tapping screw. Without removing the battery cover, you cannot get to the giblets. Next, you need to neutralize several latches. 
Then I unscrew 4 screws. 
The contact pads of the switch are hardly greased. Lubricated with ciatim.
There is not a single trimmer inside. On the one hand, it's bad. It is impossible to adjust the measurement accuracy (in which case). On the other hand, good. There are no trimmers, which means there is nothing to go astray.
In the role of the processor, a microcircuit of the "blob" type. They did not regret the compound. 
I have no comments on the quality of the soldering.
I close the device and proceed to determining the accuracy of the device.
All devices, with which I will determine the accuracy, have a cost in the range from 10,000 to 100,000 rubles. Naturally, these are not personal devices. Hardly anyone has them for personal use. Someone will be interested.
Let's check how the change is measured using B1-9 (installation for checking voltmeters) 
This setting allows you to measure the error directly as a percentage. But I will not use this convenient option. I will give all measurements in the form of a table. In my opinion, this is clearer. I set the frequency to 50Hz, bring the error regulator to zero. I just write down what the multimeter shows. 
The result is simply gorgeous. You can not pay much attention to 10mV. Firstly, the error gives the voltage induced on the wires (pickup). Secondly, in my entire life I have never had to measure voltages of this level. To measure voltages of this level, short shielded wires are required.
Among other things, this setting allows you to change the frequency of the reference signal. As a result, I got that the multimeter allows you to accurately measure a sinusoid within the range of 10-1100Hz.
And here is a comparative photo of the measured voltage of the industrial network with another fairly accurate device True RMS V7-78 (we will consider it exemplary), which costs once… more expensive than the monitored one. 
There are discrepancies. But this is a very good result. Believe me, I have been working for several years ...
The constant will be evaluated using the programmable P320 calibrator. It's simple. I connect a multimeter to the calibrator and write down what it (the multimeter) shows. All data was put into a table. 
At 420mV - 4.2V - 42V, the result is simply gorgeous. On the rest - within the declared boundaries.
Let's move on to measuring resistance.
Resistance stores P4834 and P4002 will help me.
First I bridged the probes. 
All measurement data are tabulated. 
If you do not take into account the 42MΩ limit, the error is much higher than stated (in the last digit).
The ringing diodes and the buzzer are separated into different modes. When the diodes are ringing, the battery voltage is present on the open probes. You can ring the LEDs. Under load, the voltage (naturally) drops. 
In the buzzer mode and measuring resistances, the voltage across the probes is about one volt.
These are actually measured readings.
I will check the accuracy of measuring the containers using the P5025 magazine.
I will explain some of the nuances.
1. The sample has an initial capacity, it must be taken into account.
2. When measuring capacities over 10μF, a delay in measurements is observed. I noted the delay time in the table. 
The store is limited to a capacity of 100μF. I do not have a sample for a large capacity.
I will add a few photos with electrolyte measurements. 
I wanted to know to what limit the device was designed. But I never found out. 
The specifications say that it can measure up to 200μF. As you can see from the photo, it can measure more than 10.000μF. Nice feature!
The device measured this bundle in 7 seconds. Although according to the logic of testing on a sample, I thought that he would spend at least a minute.
Frequency measurement ...
To determine the measurement accuracy, I connected the Will "TEK Stabilock 4032 to the device. I did not strain myself. The device can give out calibrated frequencies, which is very convenient. 
I apologize for the quality of the photo. The device is in the corner of the room. And with a flash, the picture quality is even worse.
All data was put into a table. (The frequency sensitivity of the device was duplicated on G3-112.)
The accuracy of the readings is clearly higher than stated. 
The frequency is measured above 10 MHz. True, the sensitivity is rather weak. We have to turn up the signal. Stopped at 34MHz. 
We return to the beginning of the review. So what made me do this review? In that topic, I made one serious omission. I did not notice the True RMS inscription at all. A distinctive feature of this multimeter is the calculation of the rms value of the measured AC voltage.
Checked with MHS-5200A. Interesting in that it can produce signals of any shape. I set the frequency to 50Hz. But there is a peculiarity. Shows only the signal swing (in my case 10V peak value). 
The waveform and the root mean square (True RMS) value were controlled using another device (who knows the price - keep quiet :))
First I applied a sinusoid. 
Then he served like this.
Then this one.
Then this one. 
And finally ... 
Super!
Conventional multimeters (give an error of more than 8%) on such waveforms start to lie a lot. 
I calibrated this device (FUYI FY9805) specifically for reviews, I like it for its contrast of numbers. But you can't insert True RMS into it: (Therefore, it is lying, if not a sinusoid.
And VICTOR VC921 did not disappoint. The Chinese did not deceive. He really can.
It's time to move on to the final part. I will highlight what I liked and did not like. The point of view is subjective.
Minuses:
- Probes cannot be quickly replaced (in case of breakage), since they are soldered directly into the device board.
- Small space for probes.
- Paley testimony in contrast to their fellows.
- Does not measure current strength (for some, this is important).
- No analogue scale.
- No display backlight.
- Not soft, medium quality probes.
Pros:
+ The indicator shows the measured values \u200b\u200b(μF, mV, ...).
+ Auto selection of measurement limits (with the ability to disable the function).
+ Made neatly and soundly.
+ You can ring the LEDs.
+ The presence of auto shutdown. The device turns off after 15 minutes.
+ The device (in terms of metrology) is simply gorgeous. True, there are some nuances.
+ Powered by two AAA elements is a definite plus (for me). I will find it always and everywhere (even on a business trip, even at home)
+ The presence of a slot for a switch on the front cover forces the device to be turned off after use.
+ Measures electrolytes with a capacity of over 10,000 μF!
+ With True RMS!
Output:
It's really worth it. Apply the coupon and you will be happy too :)
It seems everything. If you forgot something, correct it.
How to properly dispose of the information from my review, everyone decides for himself. I can only guarantee the veracity of my measurements. If you are unclear about something, ask questions. I hope at least helped someone.
That's it.
Good luck everyone!
