[introduction]Pure imitate instrument is offerred below the case that uses so extensively now in digital appearance may surprising. However, well-known, digital appearance is in modulus converter (imitate circuit is had before ADC) . Frequency from under 20 Hz the broadband imitate volmeter to 200 KHz already was used extensively in the past, and very useful still.

Pure imitate instrument is offerred below the case that uses so extensively now in digital appearance may surprising. However, well-known, digital appearance is in modulus converter (imitate circuit is had before ADC) . Frequency from under 20 Hz the broadband imitate volmeter to 200 KHz already was used extensively in the past, and very useful still.

The main technique index of broadband imitate appearance

Use contemporary operation amplifier (Op Amps) , the design of our imitate appearance can simplify greatly. The component with this design use reasonable price offers 20 Hz to 1 MHz (it is when 10 Hz – 1 DB) even bandwidth.

In ground connection end inserts resistor of 0.1 Ω to won’t show the circuit that reduces electric current in, it is not difficult to increase the capacity that gauges electric current. If appearance is of batteries power supply or safe grade 2 structures, criterion ground connection join need not be actual ground connection.

6 voltage span is respectively 1, 10, 100 MV and 1, 10, 100 V full span, and span of 4 electric current is respectively 10, 100 MA and 1, 10 A full span. This design includes detector of peak value of a broadband, can switch the peak value voltage that its sensitivity takes sine wave signal with reading or root mean square (RMS) voltage.

Can insert exterior filter to be answered in order to offer special frequency. This function still allows to use appearance as two have switch the independent amplifier of alterable gain.

This instrument will use power supply of batteries of two 9 V or device of power source of a 9-0-9 V. The electric current of every batteries is used up under 25 MA (without any glow diode (LED) indicator) , because this can cast longer service life.

Imitate appearance project — general specification

Instrument block diagram is shown 1 times like the graph.

Graph 1. Block diagram of broadband imitate appearance.

Input attenuator / voltaic mode selector is indispensible, because we want to measure the voltage that is as high as 100 V, and they cannot apply at amplifier directly. When choosing voltaic mode, detect without switch contact and electric current resistor series connection, eliminated potential error source thereby. Paid small price is need of voltaic mode operation an alone connector.

Use two operation amplifier to achieve gain

Amplifier needs about the gain ability of 1000 (60 DB) offers full span reading for 1 MV input. This comes true through using the two operation amplifier in LM4562, the gain of every operation amplifier is 31.62. LM4562 is used at high fidelity preamplifier actually, accordingly it is had low noise and low lack fidelity and the broadband is wide. Maladjusted voltage is not very hot, but can overcome in this application.

Because have two amplifier class, because this offers connector and switch very easily, so that other circuit can be inserted between two amplifier, if be in,the output end of the 2nd amplifier adds another connector, they also can use as independent amplifier.

Choose your detector: Half, ” true virtual value ” He Quanbo peak value

Must make important decision with respect to offerred detector kind, it is dc with will magnifying signal is changed, so that handle digital monitor or instrument of type of pressing with a finger. Simple detector is half average model, it tells us very few the information about signal, the voltage deflection that showing is concealed in the half-period that and the likelihood is in did not detect.

Be in complex spent another end is ” true RMS ” detector, mark is ” true ” in order to distinguish at average detector, latter gain already was adjusted the RMS cost that takes wave signal in order to read, is not the RMS value of all and other signal. If you want to know the RMS of signal is worth, this is very good, but the equipment with reasonable price is AD736, its frequency limitation is 200 KHz, and the working frequency of amplifier is as high as 1 MHz or taller.

The detector of the 3rd kind of type is detector of complete wave peak value, it can be built with reasonable price compose. Normally need measures the peak value of signal, because it may demonstrate signal cable length,medium certain part overload is mixed cut a peak. Want weaveform to was not cut apparently only wave, through dividing peak value with 1.4 or by with 0.7 find sine wave signal very easily also (although lack fidelity be as high as 10% ) RMS value. This is arranged very easily, because it needs talent of attenuator of a 3 DB,put through.

Another simple attenuator is in the 20 DB of span switch (10 times) the condition is chief between undertake interpolation, this makes the on half part that the directive of all prep above 0.5 MV on instrument of type of pressing with a finger is located in scale. Two kinds of attenuator can apply.

The detector of complete wave peak value that searchs the working frequency that already released to be as high as 1 MHz is proved to be infructuous, but the technology that comes from two improper detector through incorporating, found a solution, use another LM4562 and BF140 of two RF ambipolar transistor. Also can use of course other the dynatron that has similar or better character, but do not suit the general dynatron such as BC547/847.

The circuit of the project designs a respect

To this experiment, piece be alone description, their principle pursues (amplifier except) use double operation amplifier and 2 extremely switch, accordingly, them separate meeting is caused promiscuous. If show on single page, whole principle pursues too big and cannot identify. The power source join of operation amplifier shows only for V+ and V –, also show in power source module pass to avoid to use much long term.

Input attenuator and voltaic mode switch

If the graph is shown 2 times,the principle that inputs attenuator and voltaic mode switch pursues.

Graph 2. Input attenuator and voltaic mode switch.

Switch shows in sensitivity position. Begin to arrange hour hand shift from inferior position, switch condition is chief for voltaic mode (10 MA) , 100 V, 10 V and 1 V.

Voltaic sensor resistor (and all resistor that use in the project, unless have a specification additionally) should have ± the tolerance of 1% , accordingly it is not a cheap component, but can afford. Another kind of method is paralell connection uses resistor of Ω of a 0.15 and another value, the choice is close to 0.1 Ω . Divide metalloid case, should not wind a string otherwise, otherwise inductance may be in high frequency when introduce an error: 100 NH is 628 M Ω when 1 MHz.

Ask an attention, electric current detects resistor is inputting connector two end join as far as possible close, lest introduce extra resistance. Also lie between straight capacitance without series connection with manage. If use rated power to be 1 W or higher component, any dc component that are less than 10 A won’t pose a problem.

If use taller volts d.c. , c2 should be rating is 250 V or taller polyester film capacitor.

Fine tuning capacitor is used at adjusting attenuation in order to make its are in high frequency below correct. These values are useful to me, but capacitance special rely on a structure, accordingly you may need different value or configuration.

With the 2nd amplifier and limits switch

If the graph is shown 3 times,the principle pursues.

Graph 3. With the 2nd amplifier and limits switch.

Of switch decorate make receive signal circuit repeatedly without untapped resistor; They are adherent go up in the ground. the introduction attenuator of 3 /10/13 DB is mixed below one ” exterior filter ” switch.

Switch shows in 1 V position. Each pace transforms the gain of the 10 DB on every switch the utmost, give out 20 DB condition is chief (10) .

The low cost of feedback resistor R10 and R16 is the key that obtains wide bandwidth. They need to be close to Ω of 2.2 K as far as possible, this may be meant should undertake choosing from inside many component.

R5 and R10 can be E96 series value 71.5 Ω or 82 Ω | | 560 Ω (| | Express ” shunt-wound ” ) . R6 and R11 are 180 Ω | | 3.3 1000 Europe. R7 and R12 are 820 Ω | | 10 1000 Europe. Other combination is likely apparently. In addition, r8 and R13 can be 220 K Ω .

Be necessary to be close to place to require a cost as far as possible, depend on because of the precision of the instrument it. Should avoid to use as far as possible beforehand buy resistor, or use high grade cell; Otherwise, calibration stability will be affected.

Ask an attention, Ω of use 2.2 K and resistor of 220 K Ω undertake gain setting can produce gain to be the inphase amplifier of 1.01 (0.086 DB) feedbacking, this gain is enough and adjacent 1.

Add attenuator and exterior filter connector

3 DB (peak value arrives RMS sine wave) with 10 DB (scale amplifier) attenuator and exterior filter switch are shown 4 times like the graph.

Graph 4.  3/10/13 DB attenuator and exterior filter connector pursue [click zoom] .

With before, be necessary to measure resistor and choose to be close to the resistor that requires a cost. Below this kind of circumstance, can use E12 value, but cost is to be – 13 DB network increases a resistor.

The capability that checks E12 series resistor to offer place to need attenuation is very useful. Express fruit of 1 indication finish.

Express 1. Compare the error of function as attenuation.

Damply Decibel	Attenuation comparing	Resistor of the upper arm	Leave brachial resistance	Rate Below / (below + go up)	Wrong ％	Error decibel
3	0.7071	3.3k	8.2k	0.7130	– 0.84	– 0.062
10	0.3162	3.9k	1.8k	0.3158	0.14	0.012
13	0.2236	13.5k	3.9k	0.2241	– 0.24	0.021
3 decibel rehabilitate	0.7071	3.382k	8.2k	0.7080	– 0.12	– 0.011

Resistor of use measured value, can through adding a low cost resistor establishs ties with any too low resistor will change an error. For example, if the resistor of 3 DB is 3.3 K Ω and 8.2 K Ω fitly, the 82 Ω that can establish ties with 3.3 K Ω through adding comes repair error.

Toggle switch is used in this network very convenient, also can use toggle switch or rotary switch of course.

Peak value detector and appearance

Peak value detector is shown 5 times like the graph.

Graph 5.  The chart of detector of indication peak value [click zoom] .

It has 3 functions that ensure the broadband is wide:

? The resistance in these circuit is far under connect general reason condition
? Class uses diode of Xiao Te radical
? Two are shot extremely follow implement the load that is used at changing the 2nd class to output end

BAT54 diode can be replaced with BAT85. If span switch setting is incorrect, d3 can protect appearance to avoid the effect that has sufferred big electric current.

The BF240 device that uses in prototype can be replaced to have the other equipment of very similar character. Although it is an old equipment, but it still can be used and use at FM radio RF phase, the other equipment that is used at same service accordingly may be applicable also. Remember please, the current equipment such as BC547 and 2N3904 is not applicable.

In addition, r23 and R26 can be comprised by two 1k resistor, r32 is OK also comprise by 10k and 56k resistor paralell connection. The choice that its are worth is to make beforehand buy resistor is adjusted go up in appearance with input of 1 V RMS when 1 KHz read take 1 V and apply 3 DB attenuator, should control in its orbital half.

Can join monitor of a number will replace R32, RV1 and appearance M.

Power source

Power source circuit is shown 6 times like the graph.

Graph 6.  The chart of indication power source.

100 NF capacitor should stand by the IC of side of line power source to cite crural installation as far as possible. If walk along a line to cite a base to IC first,arrive again capacitance, can have the inductance that does not need and capacitance series, the capacitance resonance that uses 100 NF does not need too much inductance.

The function of project of broadband imitate appearance

Unless eligible (for example, through ” depend on layout ” ) , otherwise the number is based on archetypal measured value.

? Input resistor (all voltage limits) : ± of 1 M Ω 1%

? Input capacitance: 20 PF (depend on layout)

? Frequency answers: Arrive from 20 Hz 1 MHz evenness: It is when 10 Hz and 1.2 MHz – 1 DB.

? Voltage limits: 10 – of 1 – 1 – of 100 MV – 10 – 100 V; Precision depends on span switch and attenuator resistor approach level with what its are worth correctly.

? Shed output continuously: In voltage input end brings to bear on the 1 V RMS when 1 KHz, limits switch setting is 1 V, there is 3 DB attenuator in circuit, r29 and the dc that R30 join nods output voltage to should arrive in the V inside 0.95 limits 1.05 V. If not be, the value that adjusts R16 a little please (do not correct big mistake) .

? Voltaic limits: 1 A of – of 10 – 100 MA. Precision depends on the precision of limits switch and electric current detect resistor R1 approachs level with what be worth correctly.

? Shed output continuously: In electric current input end brings to bear on the 1 A RMS when 1 KHz, limits switch setting is 100 MV, there is 3 DB attenuator in circuit, r29 and the dc that R30 join nods output voltage to should arrive in the V inside 0.95 limits 1.05 V. If not be, the value that adjusts R1 a little please (do not correct big mistake) .

You can contain ± of 8 Ω through using 1% resistor (only dissipation 0.125 W, accordingly? W part is possible) the frequency amplifier that establishs ties with output and voltaic input will produce 1 A. Adjust input signal n to obtain 8 V RMS in order to be on resistor of 8 Ω .

If pursue,the frequency that every limits installs is answered 7, 8, 9 show with 10.

Graph 7.  The frequency that the 1 V inside 1 V limits inputs is answered [click zoom] .

Graph 8.  The frequency that the 100 MV inside 100 MV limits inputs is answered [click zoom] .  


Graph 9.  The frequency that the 10 MV inside 10 MV limits inputs is answered [click picture enlarge]

Graph 10.  The frequency that the 1 MV inside 1 MV limits inputs is answered [click zoom] .

1.2The response that MHz is in exceeds the range of scanner, because this uses a signal generator,undertake metrical to its. Inside this limits, as a result of small input and tall gain, walk along the meeting on the line to appear a few noise. Graph 11 showed the ammeter response when 100 MA.

Graph 11.  The ammeter response when 100 MA [click picture enlarge] .

Optional exterior filter

The input resistor of exterior filter should be 10 K Ω or bigger, output resistor should be 1 K Ω or smaller.

Avoid duty statement: The article is reprint an article, reprint this article purpose to depend on passing more information, the person that copyright puts in original work ‘s charge is all. If involve work copyright issue,article place uses video, picture, written language, contact please small make up undertake handling.