Comparison UNI-T UT139C vs Mastech MS8239C

The upper limit of the lower sub-range in which the device can measure DC voltage (see "Type of voltage").

The operating ranges of modern multimeters and other measuring instruments are usually divided into subranges. This is done for accuracy and convenience when measuring: for example, to assess the quality of AA batteries, you can set the subrange “up to 3 V” — this will give an accuracy of up to tenths, or even hundredths of a volt, unattainable when measuring with a higher threshold. The minimum constant voltage describes exactly the lower subrange, designed to measure the smallest voltage values: for example, if 2000 mV is indicated in this paragraph, this means that the lower subrange covers values \u200b\u200bup to 2000 mV (i.e. up to 2 V).

It is worth choosing according to this indicator taking into account the specifics of the planned application: for example, a device with low rates can be useful for delicate work, such as repairing computers or mobile phones, but for servicing the on-board electrical network of a car, especially high voltage sensitivity is not required.

The upper limit of the lower sub-range in which the device can measure AC voltage (see "Type of voltage").

The operating ranges of modern multimeters and other measuring instruments are usually divided into subranges. This is done for accuracy and convenience in measurements: for example, to test a transformer that should output 6 V, it makes sense to set a subrange with an upper threshold of 10 V. This will ensure accuracy up to tenths of a volt, unattainable when measuring with a higher threshold. The minimum constant voltage describes exactly the lower subrange, designed to measure the smallest voltage values: for example, if 2000 mV is indicated in this paragraph, this means that the lower subrange covers values \u200b\u200bup to 2000 mV (i.e. up to 2 V).

If the device is purchased for measurements in stationary networks — household at 230 V or industrial at 400 V — you can ignore this parameter: usually, the minimum subranges are not used. But to work with power supplies, step-down transformers and various “thin” electronics served by low voltage alternating current, it makes sense to choose a model with a lower minimum voltage. This is connected not only with the measurement range: a low threshold, usually, indicates a good measurement accuracy at low voltages in general.

The upper limit of the lower sub-range in which the device can measure direct current (see "Type of current").

The operating ranges of modern multimeters and other measuring instruments are usually divided into subranges. This is done for accuracy and convenience in measurements: the lower the subrange, the smaller values it covers, the higher the measurement accuracy at low current values. The minimum direct current describes exactly the lower range, designed for the weakest current values: for example, if the characteristics in this paragraph indicate 500 μA, this means that the lower subrange allows you to measure currents from 0 to 500 μA.

It is worth choosing according to this indicator taking into account the specifics of the planned application: for example, a device with low rates can be useful for delicate work, such as repairing computers or mobile phones, but for servicing the on-board electrical network of cars, especially old ones, especially high current sensitivity is not required.

The upper limit of the lower sub-range in which the device can measure alternating current (see "Type of current").

The operating ranges of modern multimeters and other measuring instruments are usually divided into subranges. This is done for accuracy and convenience in measurements: the lower the subrange, the smaller values it covers, the higher the measurement accuracy at low current values. The minimum alternating current describes exactly the lower range, designed for the weakest current values: for example, if the characteristics in this paragraph indicate 500 μA, this means that the lower subrange allows you to measure currents from 0 to 500 μA.

It is worth choosing according to this indicator taking into account the specifics of the planned application: for example, a device with low rates can be useful for delicate work, such as repairing computers or mobile phones, but especially high current sensitivity is not required for servicing household electrical networks.

The upper limit of the lower sub-range in which the device can measure resistance.

The operating ranges of modern multimeters and other measuring instruments are usually divided into subranges. This is done for accuracy and convenience in measurements: the lower the subrange, the smaller the values it covers, the higher the accuracy of measurements at low resistance values. The minimum resistance describes exactly the lower range, designed for the weakest current values: for example, if the characteristics in this paragraph indicate 500 Ohms, this means that the lower subrange allows you to measure resistance from 0 to 500 Ohms.

When choosing for this indicator, you need to consider how important it is for you to accurately measure small resistances. At the same time, we note that the 500 Ohms given in the example are a fairly good indicator, indicating a fairly solid resistance measurement accuracy; in relatively inexpensive multimeters, this indicator can be 2.5 or even 10 kΩ, which ensures accuracy at best up to several tens of ohms.

The highest resistance that the instrument can effectively measure.

When choosing according to this indicator, you must first take into account the largest resistances that are supposed to be measured. And if we are talking about an analogue device (see "Type"), you must also remember that as you approach the maximum resistance, the measurement accuracy drops sharply. This is due to the peculiarities of measuring and grading the scale in such devices: for example, with a maximum resistance of 1 MΩ, the division value in the range of 0 – 2 kΩ can be 0.2 kΩ, in the range of 2 – 6 kΩ — 0.5 kΩ, in the range of 6 – 10 kOhm — already 1 kOhm, and closer to the maximum this figure can reach tens and even hundreds of kilo-ohms. Therefore, it is worth choosing an analogue device in such a way that its maximum resistance is at least 10 times higher than the largest resistances that are planned to be measured — only under this condition is a more or less acceptable measurement accuracy ensured.

The highest number that the DMM display can display (see "Type").

This indicator determines the range in which measurements can be taken without changing the settings. So, if the maximum number is 1999, then the measurement can be made in the range from 0 to 1999 of the selected units of measure — for example, from 0 to 1999 V if volts are selected, from 9 to 1999 mA (1.999 A) if milliamps are selected, etc. At the same time, 1999 and less for modern measuring instruments are considered a rather modest indicator, from 2000 to 3999 — average, 4000 – 9999 — not bad, and in the most advanced models this number exceeds 10000.

Note that the maximum displayed number is directly related to the display capacity — see below.

The digit capacity of the display installed in the digital instrument (see "Type").

Bit depth is the number of characters that can be displayed on the screen at the same time. The maximum displayed number directly depends on it (see above): for example, if the digit capacity is 4, then the device has a display for 4 full digits and is able to display a number up to 9999 inclusive. However, there are also more specific markings — with a fraction, for example, 3 1/2 or 4 3/4. This means that the largest (left) digit in this model is incomplete and the maximum digit that it can display is less than 9. Specifically, such marking is deciphered as follows: an integer means the number of full digits, the numerator of a fraction is the maximum number displayed in an incomplete digit, the denominator is the total number of values supported by an incomplete digit. Considering the above examples, 3 1/2 means a four-digit display with the maximum number in 1999: three full digits with a maximum value of 9, plus one partial digit with a maximum value of 1 and two options (1 and 0). Similarly, 4 3/4 corresponds to the maximum number 39999, with 4 options for values in the partial digit (0, 1, 2, 3).

- Checking the transistor. The ability to use the device to test transistors, more precisely, the presence of an appropriate mode in the design of the device. Technically, the performance of a transistor can be checked to a certain extent with an ordinary ohmmeter, for this there is an appropriate technique. Nevertheless, it is much easier to use a special mode - just connect the transistor to the multimeter in an appropriate way, and the device will automatically give data on the health or malfunction of the part (and sometimes additional characteristics for it). Most often, for such measurements, there is a special block on the case with a set of sockets for transistor outputs (with separate sets of sockets for pnp and npn types).

- Checking the diode. The presence of a special diode test mode in the design of the multimeter. The principle of a diode is to allow electric power to flow in only one direction; therefore, the serviceability of such a part itself can be determined without a special mode, for example, in the mode of a conventional ohmmeter, “continuity” of the circuit (see below), or in some other ways. However, special mode is often more convenient - both due to the simplicity of the procedure itself, and due to the fact that many devices in this mode are also able to measure the forward voltage drop across the diode (the lowest voltage required to pass power in the forward dir...ection).

— "Continuity" of the chain. Possibility of operation of the device in the "continuity" mode of the circuit - checking the presence of contact between two selected points. This mode differs from the usual check with an ohmmeter in that the presence of a contact is accompanied by an audible signal (hence the name). Such a signal saves the user from having to look at the scale of the device every time to clarify the presence or absence of contact, and this greatly speeds up the work and can be very useful if you need to “ring out” many sections at once.

- Meander generator. Ability to operate the device in the meander generation mode - a signal with a rectangular pulse shape and a duty cycle (see above) at level 2. The graph of such a signal looks like a set of rectangular peaks and dips of the same length. Meander is a regular signal format for modern digital technology; a signal of this type, generated by a multimeter, is used to test microcircuits, logic elements, amplifiers and other similar elements and circuits (for performance, signal flow, etc.).

— Non-contact detection (NCV). Ability to detect live parts without direct contact with them. This method of detection is as safe as possible, besides, it allows you to find elements hidden from the eye: for example, using a device with this function, you can detect wiring in walls and determine places where you can drill without fear of damaging the wire.

— True RMS. Ability to measure with the True RMS device - the true RMS value of the strength of the alternating power (see "Type of power"). The strength of the alternating power is determined not by the actual value (it will be different at each moment of time), and not by the maximum amplitude (after all, the maximum values also occur only at certain points in time), but by the root mean square. At the same time, in devices that do not support True RMS, this value is displayed as follows: the alternating power is rectified, its value is determined and multiplied by a factor of 1.1 (this is due to the mathematical features of the measurements). However, this method is only suitable for an ideal sinusoid; with a distorted signal, it gives a noticeable, and often even unacceptably high error. Distortions are found in almost any AC network, which can lead to serious measurement errors and subsequent problems (for example, to the selection of too “weak” automatic fuse). True RMS technology takes into account all these features: devices bearing this marking are able to accurately measure AC RMS power, regardless of how its shape corresponds to a perfect sine wave.

- Auto-selection of the measuring range. A function that allows the device to automatically select the optimal measurement range - so that the result is displayed on the screen as accurately as possible. This function is found only in digital instruments (see "Type"). Note that when using it, the user will still have to set certain basic settings - for example, “direct power, power, milliamps” or “alternating power, voltage, volts”. However, the device will perform a more precise setting itself: for example, to measure voltage in hundreds of volts, the range 0 - 1000 V can be used with an accuracy of 5 V, and when a 1.5 V battery is connected, the device will automatically switch to the range 0 - 12 V and display the result is already accurate to tenths of a volt. At the same time, the design may also provide for a completely manual measurement mode, with a range selection at the request of the user, however, the presence of such a mode will not hurt to clarify separately.

- Auto power off. The function of automatically switching off the Meter after a period of inactivity helps to conserve the charge of the used batteries.