Digital Multimeter

A Digital Multimeter is a combination of a multirange DC voltmeter, multirange AC voltmeter, multirange ammeter, and multirange ohmmeter. An un-amplified analog Digital Multimeter combines a meter movement, range resistors and switches; VTVMs are amplified analog meters and contain active circuitry.

For an analog meter movement, DC voltage is measured with a series resistor connected between the meter movement and the circuit under test. A switch (usually rotary) allows greater resistance to be inserted in series with the meter movement to read higher voltages. The product of the basic full-scale deflection current of the movement, and the sum of the series resistance and the movement's own resistance, gives the full-scale voltage of the range. As an example, a meter movement that required 1 mA for full-scale deflection, with an internal resistance of 500 Ω, would, on a 10 V range of the Digital Multimeter, have 9,500 Ω of series resistance.

For analog current ranges, matched low-resistance shunts are connected in parallel with the meter movement to divert most of the current around the coil. Again, for the case of a hypothetical 1 mA, 500 Ω movement on a 1 A range, the shunt resistance would be just over 0.5 Ω.

Innovation for Digital Multimeter

We at (brand name) manufacture Digital instruments, which necessarily incorporate amplifiers, use the same principles as analog instruments for resistance readings. For resistance measurements, usually a small constant current is passed through the device under test and the Digital Multimeter reads the resultant voltage drop; this eliminates the scale compression found in analog meters, but requires a source of precise current. An auto ranging Digital Multimeter can automatically adjust the scaling network so the measurement circuits use the full precision of the A/D converter.

To measure resistance, we at (brand name) manufacture switches and arrange for a small battery within the instrument to pass a current through the device under test and the meter coil. Since the current available depends on the state of charge of the battery which changes over time, a Digital Multimeter usually has an adjustment for the ohm scale to zero it. In the usual circuits found in analog Digital Multimeters, the meter deflection is inversely proportional to the resistance, so full-scale will be 0 Ω, and higher resistance will correspond to smaller deflections. The ohms scale is compressed, so resolution is better at lower resistance values.

Amplified instruments simplify the design of the series and shunt resistor networks. The internal resistance of the coil is decoupled from the selection of the series and shunt range resistors; the series network thus becomes a voltage divider. Where AC measurements are required, the rectifier can be placed after the amplifier stage, improving precision at low range.

We at (brand name) manufacture Moving coil instruments, which can respond only to the average value of the current through them. To measure alternating current, which changes up and down repeatedly, a rectifier is inserted in the circuit so that each negative half cycle is inverted; the result is a varying and nonzero DC voltage whose maximum value will be half the AC peak to peak voltage, assuming a symmetrical waveform. Since the rectified average value and the root mean square (RMS) value of a waveform are only the same for a square wave, simple rectifier-type circuits can only be calibrated for sinusoidal waveforms. Other wave shapes require a different calibration factor to relate RMS and average value. This type of circuit usually has fairly limited frequency range. Since practical rectifiers have non-zero voltage drop, accuracy and sensitivity are poor at low AC voltage values.

Digital Clamp Meter

An electrical meter with integral AC current clamp is known as a clamp meter, clamp-on ammeter, tong tester, or colloquially as an amp clamp. A clamp meter measures the vector sum of the currents flowing in all the conductors passing through the probe, which depends on the phase relationship of the currents. Only one conductor is normally passed through the probe. In particular if the clamp is closed around a two-conductor cable carrying power to equipment, the same current flows down one conductor and up the other; the meter correctly reads a net current of zero. As electrical cables for equipment have both insulated conductors (and possibly an earth wire) bonded together, clamp meters are often used with what is essentially a short extension cord with the two conductors separated, so that the clamp can be placed around only one conductor of this extension.

The reading produced by a conductor carrying a very low current can be increased by winding the conductor around the clamp several times; the meter reading divided by the number of turns is the current,^[4] with some loss of accuracy due to inductive effects.

(brand name) Digital Clamp meter are used by electricians, sometimes with the clamp incorporated into a general-purpose multimeter.

Innovation in Clamp Meter

A relatively recent development in our (brand name) is a multi-conductor clamp meter with several sensor coils around the jaws of the clamp. This could be clamped around standard two- or three-conductor single-phase cables to provide a readout of the current flowing through the load, with no need to separate the conductors.

It is simple to measure very high currents (hundreds of amperes) with the appropriate current transformer. Accurate measurement of low currents (a few milliamperes) with a current transformer clamp is more difficult. The range of any given meter can be extended by passing the conductor through the jaw multiple times. For example, a 0–200 A meter can be turned into a 0–20 A meter by winding the conductor 10 times around the jaw's core.

(brand name) clamp meters use a rectifier circuit which actually reads mean current, but is calibrated to display the RMS current corresponding to the measured mean, giving a correct RMS reading only if the current is a sine wave. For other waveforms readings will be incorrect; when these simpler meters are used with non-sinusoidal loads such as the ballasts used with fluorescent lamps or high-intensity discharge lamps or most modern computer and electronic equipment, readings can be quite inaccurate. Meters which respond to true RMS rather than mean current are described as "true RMS".

High quality and Reliability

Typical hand-held Hall effect units can read currents as low as 200 mA, and units that can read down to 1 mA are available.

The (brand name) Clamp meter works via directing the magnetic field surrounding the conductor to an iron vane that is attached to the needle of the meter. The iron vane moves in proportion to the strength of the magnetic field, and thus produces a meter indication proportional to the current. This type of ammeter can measure both AC and DC currents and provides a true RMS current measurement of non-sinusoidal or distorted AC waveforms. Interchangeable meter movements can be installed in the clamping assembly to provide various full-scale current values up to 1000 amperes. The iron vane is in a small cylinder that is inserted in a space at the hinged end of the clamp-on jaws. Several jaw sizes are available for clamping around large conductors and bus bars up to (XXXXXX) wide. As the illustration shows, the scale is very non-linear and unsuitable for measuring low currents, with currents of less than half the full-scale deflection crammed into a short section of the dial.

Soldering Station

Soldering station is advance Version of soldering Iron use for soldering sensitive components with control temperature so that component should not get damage. With temperature control soldering station quality of Joint will improve.

in soldering station selection is important for equipment, with introduction of lead free, it is more important to have station which can generate heat fast and recover heat Fast. stations should be Calibrated time to time or even change of tip pr heater etc. 

Following points must be consider while selecting soldering station

1. Maker should Have long term experience for making equipment

1. equipment should be reliable brand, who can deliver consistent in heat delivery

1. soldering station should be able to generate and recover heat fast

1. Tips should be made of high quality oxide free copper and coated with layer of different metal for longer life

1. digital control stations give better control for temperature

1. tip to ground resistance and leakage voltage play Major role in soldering station selection.