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1．Average responding or TRMS (True Root Mean Square)
The DMM is capable of measuring ac signals by operating as either an average responding or a true rms-to-dc converter. As its name implies, an average responding converter computes the average absolute value of an ac (or ac and dc) voltage or current by full wave rectifying and low-pass filtering the input signal; this will approximate the average. The resulting output, a dc “average” level, is then scaled by adding (or reducing) gain; this scale factor converts the dc average reading to an rms equivalent value for the waveform being measured. For example, the average absolute value of a sine-wave voltage is 0.636 that of VPEAK; the corresponding rms value is 0.707 times VPEAK. Therefore, for sine-wave voltages, the required scale factor is 1.11 (0.707divided by 0.636). In contrast to measuring the “average” value, true rms measurement is a “universal language” among waveforms, allowing the magnitudes of all types of voltage (or current) waveforms to be compared to one another and to dc. RMS is a direct measure of the power or heating value of an ac voltage compared to that of dc: an ac signal of 1 volt rms will produce the same amount of heat in a resistor as a 1 volt dc signal. Mathematically, the rms value of a voltage is defined (using a simplified equation) as:
This involves squaring the signal, taking the average, and then obtaining the square root. True rms converters are “smart rectifiers”: they provide an accurate rms reading regardless of the type of waveform being measured. However, average responding converters can exhibit very high errors when their input signals deviate from their precalibrated waveform; the magnitude of the error will depend upon the type of waveform being measured.
As an example, if an average responding converter is calibrated to measure the rms value of sine-wave voltages, and then is used to measure either symmetrical square waves or dc voltages, the converter will have a computational error 11% (of reading) higher than the true rms value (see Table I ).
Table I. Error Introduced by an Average Responding Circuit When Measuring Common Waveforms
2.AC+DC TRMS
Compare with AC TRMS DMM, AC plus DC TRMS DMMhas stricter requirements on IC, and it represents the higher level. During practice measurement, as many tested signal has DC element, for example, the signal of half-wave rectification, if you only measure the TRMS of AC, the neglect of DC element will lead to error, so the most desirable DMM for AC measurement is AC plus DC TRMS DMM.
3．DIGITEK’s Contributions
Now that the TRMS DMM is the really reliable and desirable measurement instruments in practical use, why at present the DMM sold in quantity are average value DMM? The main reason is: the price of previous TRMS DMM is much higher than average-value DMM, so lead to the TRMS DMM cannot be popularly used. Now Digitek exert their technical advantage, provided the high quality and performance and also the cheapest and competitive TRMS DMM for the user, and created very favorable future for the popularization of TRMS DMM.
Smart DMM
(Function Auto-selective DMM---IDIOT’S DMM)
The newly designed SD (Smart DMM) series of Digitek Company is made out as per Digitek’s own patent.
The invention starts the new era in which mltimeters auto select measurement functions.
Multimeter has seen the following 3 eras:
1. Analogue multimeter,
2. Manual range digital multimeter
3. Auto range digital multimeter.
Nowadays, Digitek has developed it to:
4. The era of smart digital multimeters which are able to auto select measurement functions.
This technical invention is what many people and many companies ever hoped to achieve, now we ve done!
The appearance of new technology and new product will open a new market.
The SD series of Digitek make DMM even suitable for unprofessional persons. Whatever kind of person you are, you can use it easily just by picking it up. Nowadays all kinds of electronic products are spread all over families, schools, stores and automobiles etc, Smart DMM will be a mirror for measuring instruments, as a portable measuring tool featuring its high smartness, extremely simple and convenient usage, high safety and reliability, accurate and intuitionistic readings. Larger potential market is forthcoming.
While we are applying our patent techniques in new products, we are further developing more and more varieties to meet customers is need. At present we want to share our success with you by introducing our new products. We expect to push it everywhere over the world through the cooperation with you. The current product is only used to show some new ideas, but it does not mean all the SDMMs. Besides selling our current product, you are welcome to use our technology patent to cooperate in OEM and ODM, and then make products specially for your market and users with different outlines and functions. Let is go hand in hand to step in the new era of SDMM.
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