CN203858291U - Measuring circuit for high frequency current - Google Patents

Abstract

Disclosed is a measuring circuit for a high frequency current. The measuring circuit comprises a sampling circuit, an effective value converting circuit, a CPU, and a display circuit, the sampling circuit is formed by current mutual induction coils and sampling resistors and used for converting the detected high frequency current to sampling signals, the effective value converting circuit is connected with the sampling circuit and is used for receiving the sampling signals, performing multiplication operations of the sampling signals, and outputting effective value signals, the CPU is connected with the effective value converting circuit and is used for receiving the effective value signals and outputting digital signals after internal A/D conversion, proportion calculation and correction of the effective value signals, and the display circuit is connected with the CPU and is used for receiving the digital signals and displaying the digital signals. According to the measuring circuit, the effective value conversion technology is employed, the structure is simplified, the cost is reduced, the measuring range is large, the measuring precision is high, the reading is visual, a thermoelectric high frequency ammeter can be replaced, and the output power of high frequency operation equipment is tested.

Description

A kind of metering circuit of high-frequency current

Technical field

The utility model relates to the metering circuit for high frequency surgical equipment output current, belongs to electronic technology field.

Background technology

According to the test request to high frequency surgical equipment output power, need to adopt the satisfactory high frequency ammeter of performance and noninductive resistance to measure.The minimum output frequency of high frequency surgical equipment is 200kHz, uses before this thermoelectric (al) type high frequency ammeter to measure always.Although the accuracy of thermoelectric (al) type high frequency ammeter is high, overload capacity is poor, easily occurs to burn table, and be subject to the restriction of range in measurement, needs to change frequently table in process, and complex operation is also uneconomical.In view of current RMS-DC converter technology maturation, and precision is also very high, therefore completely likely finds the alternative original thermoelectric (al) type high frequency ammeter of a kind of novel high frequency current measurement circuit and measures.

Utility model content

The purpose of this utility model is to overcome the deficiency of existing thermoelectric (al) type high frequency ammeter, a kind of metering circuit of high-frequency current is provided, replace poor, the complex operation of overload capacity and expensive thermoelectric (al) type high frequency ammeter, adopt the measurement problem of RMS-DC converter technology solution high-frequency current, the effect that reach range extension scope, improves measuring accuracy, reduces costs.

For achieving the above object, the technical solution adopted in the utility model is:

A metering circuit for high-frequency current, is characterized in that: described metering circuit comprises:

Sample circuit, is made up of Current Mutual Inductance coil and sampling resistor, and tested high-frequency current is become to sampled signal;

RMS-DC converter circuit, is connected with described sample circuit and receives described sampled signal, and this sampled signal is carried out to multiplying output effective value signal;

CPU, is connected with described RMS-DC converter circuit and receives described effective value signal, by this effective value signal through inner A/D change, ratio calculate and proofread and correct after output digit signals;

Display circuit, is connected with CPU and receives described digital signal, and this digital signal is shown.

As further improvement, described RMS-DC converter circuit is the negative-feedback circuit of the first multiplier, the second multiplier and differential amplifier composition, wherein, the first multiplier be input as described sampled signal, output is by the in-phase input end of integrating capacitor access differential amplifier, the input and output of the second multiplier connect respectively output terminal and the inverting input of differential amplifier, differential amplifier output effective value signal, and this effective value signal is the root-mean-square value of the sampled signal of input.

As further improvement, described sampled signal is high frequency low voltage signal, and described effective value signal is differential voltage direct current signal.

As further improvement, the first described multiplier and the second multiplier are AD834, and described differential amplifier is LF353 intermediate frequency transport and placing device, and described CPU is C8051F350.

Compared with prior art, the utlity model has following advantage:

1, adopt RMS-DC converter technology, electronic circuit substitutes thermoelectric (al) type high frequency ammeter, simplifies the structure, and has reduced cost;

2, range ability large (Imax≤2A), precision is high, reading is directly perceived.

Brief description of the drawings

Fig. 1 is structural representation block diagram of the present utility model.

Fig. 2 is the structured flowchart of RMS-DC converter circuit.

Fig. 3 is the circuit theory diagrams of RMS-DC converter circuit.

Fig. 4 is signal processing flow schematic diagram of the present utility model.

Embodiment

The utility model adopts RMS-DC converter technology to solve the measurement problem of high-frequency current, refer to Fig. 4, the high-frequency current of high frequency surgical equipment is delivered to sampling resistor through Current Mutual Inductance coil and is become low pressure sampled signal, be effective value signal by the RMS-DC converter circuit conversion being formed by two AD834, then deliver to CPU inside and carry out AD conversion, ratio calculating and proofread and correct, and show by display circuit.

Below in conjunction with accompanying drawing, the utility model is described in further detail.

First consult Fig. 1 structural representation block diagram of the present utility model.The metering circuit of diagram high-frequency current comprises sample circuit, RMS-DC converter circuit, CPU and display circuit.

Described sample circuit is made up of Current Mutual Inductance coil and sampling resistor, and tested high-frequency current is become sampled signal Ui by it, and this sampled signal Ui is high frequency low voltage signal.

Refer to Fig. 2, described RMS-DC converter circuit is connected with described sample circuit, and its sampled signal Ui being received by described sample circuit carries out multiplying output effective value signal U ₀, this effective value signal U ₀for differential voltage direct current signal.

Described RMS-DC converter circuit is the negative-feedback circuit of the first multiplier U1, the second multiplier U2 and differential amplifier U3 composition, and wherein, the first multiplier U1 and the second multiplier U2 are AD834, and described differential amplifier U3 is LF353 intermediate frequency transport and placing device.The first multiplier U1 is input as the low pressure high frequency sampled signal Ui on described sampling resistor, and output is by integrating capacitor C _aVthe in-phase input end of access differential amplifier U3, output signal is the input of the second multiplier U2 connects the output terminal of differential amplifier U3, and output connects the inverting input of differential amplifier U3, and the input signal of the second multiplier U2 is the output signal U of differential amplifier U3 ₀, output signal is differential amplifier U3 output effective value signal U ₀, due to output homophase and the inverting input of access differential amplifier U3 respectively of the first multiplier U1 and the second multiplier U2, have thereby: i.e. this effective value signal U ₀for root-mean-square value---the effective value of sampled signal Ui of input.

The emphasis that the RMS-DC converter circuit being made up of AD834 is this patent.The advantage of this circuit is: as long as multiplier (being mainly the first multiplier U1) frequency response is enough high, and more than AD834 can reach 500MHz, differential amplifier U ₃open-loop gain is large (> 10 enough ⁴), this circuit dynamic range is quite wide.Precision is mainly derived from U ₁～U ₃imbalance, can add imbalance regulate eliminate.

Described CPU is C8051F350, is connected and receives described effective value signal U with described RMS-DC converter circuit ₀, by this effective value signal U ₀output digit signals after inner A/D conversion, ratio are calculated and proofreaied and correct.

Described display circuit is connected with CPU and receives described digital signal, and this digital signal is shown.

Below in conjunction with embodiment, the utility model is illustrated in detail.

Figure 3 shows that an embodiment of the present utility model, be described as follows:

1, sample circuit:

High-frequency current signal is inputted by Current Mutual Inductance coil coupling, due to the full be input as ± 1V of amplitude of AD834 multiplier, in order to control output accuracy, sampling resistor is divided into 3 grades, is respectively 4 Ω, 5 Ω, 28 Ω.The selection of sampling resistor be CPU automatically identify control corresponding relay switch.

2, RMS-DC converter circuit:

2.1 first multiplier U1 and the second multiplier U2 output reversal connection, as shown in Figure 3, composition difference output type, in circuit, loading resistance (R is wanted in two multiplier outputs ₁₂, R ₁₃) be converted into voltage (difference).

The transition function of 2.2AD834

$I_{W_1}-I_{W_2}=\frac{(x_1-x_2)(y_1-y_2)}{V^2}\×4\mathrm{mA}$

Owing to being collector (W1, W2) output, respectively add that the output voltage signal drawing after (connecing positive supply) pull-up resistor is reverse, for:

$V_{W_1}-V_{W_2}=\frac{(x_1-x_2)(y_1-y_2)}{V^2}\×4\mathrm{mA}\×{2R}_L$

As Fig. 3 connection, x ₁ground connection (0v), y ₂ground connection (0v),

$\begin{array}{c}{V}_{W_1}-V_{W_2}=x_2{y}_1{R}_L\×8\left(\mathrm{mA}\right)/V_2\\ =\frac{{\left(V_i\right)}^2{R}_L}{V^2}\×8\mathrm{mA}=8\frac{{\left(V_i\right)}^2{R}_L}{V^2}\left(\mathrm{mA}\right)\end{array}$

When getting R _l=100 Ω, i.e. R ₁₂=R ₁₃=100 Ω,

$V_{W_1}-V_{W_2}=0.800\frac{{\left(V_i^{\′}\right)}^2}{V}---\left(V\right)$

In the time of input 1v, $V_{W_1}-V_{W_2}=0.800V=800\mathrm{mv}$

This is maximum mean value/effective value amplitude.

2.3 peak value input V' _ip

Because output constant current source electric current is 8.5mA, for reducing distortion, input signal peak value must not make output current be greater than 8.5mA.(when the input of 1V full scale, producing input current 4mA)

$\frac{{\left({V^{\′}}_{\mathrm{ip}}\right)}^2}{V^2}\×4\mathrm{mA}=8.5\mathrm{mA},$ ?

$V_{\mathrm{ip}}^{\′}\≤\sqrt{\frac{8.5\mathrm{mA}}{4\mathrm{mA}}}\×1^v\≈{1.5}^{\mathrm{vp}}$

Representative value is 1.3 ^vp, different reasons is mainly accuracy requirement.Input signal need obtain through resistance R 5, R6, R7, R8 dividing potential drop

$\begin{array}{c}{V}_{\mathrm{ip}}=\frac{200\mathrm{\Ω}+68\mathrm{\Ω}}{68\mathrm{\Ω}}\×V_{\mathrm{ip}}^{\′}\\ =\frac{268\mathrm{\Ω}}{68\mathrm{\Ω}}\×(1.3~1.6)\mathrm{Vp}\\ =5.12~6.2\mathrm{Vp}\end{array}$

The peak factor of the solidifying pattern of high frequency surgical equipment face is 6 to the maximum, and effective value is less than 1A, and Current Mutual Inductance coil no-load voltage ratio is 5, and sampling resistor is 5 Ω, estimates V _ip≤ 6 ^vp, can meet the demands.In the time of input watt current 2A, peak factor can reach 3, meets that electric knife is pure highly necessary to be asked.If cut the maximum 1.5A of 1 pattern output current mixed, peak factor can reach 4.5.For improving peak factor, can suitably reduce sampling resistor.

2.4 input balance resistance R9, R10

Under small-signal, AD834 input resistance R _iabout 25k Ω, accesses equivalent resistance and answers <1%R _i≈ 250 Ω (anti-biasing current affects); Get divider resistance 200 Ω, 68 Ω and seal in 24 Ω, signal end access resistance 200 Ω ∥ 68 Ω+24 Ω ≈ 74.75 Ω, desirable 75 Ω of balance resistance, deviation 0.34%, the imbalance causing can be not large.Access resistance 75 Ω are only R _i0.3%, also little to effect of signals.

2.5 power supply dropping resistor R11 and pull-up resistor R12, R13

At It _(max), still require V when the=14mA × 2 (two multiplier reasons) _t>4 ^v,

$R11<\frac{8^v-4^v}{2\&times;14\mathrm{mA}}\&ap;143\mathrm{\&Omega;}$

Desirable 120 Ω/130 Ω, the V of R11 _{t (min)}=8 ^vΩ/130 ,-2 × 14mA × 120 Ω ≈ 4.64 ^v/ 4.36 ^v> 4 ^v

Work as I _tminimum 2 × 8mA, V _{t (max)}=8 ^vΩ/130 ,-2 × 8mA × 120 Ω ≈ 6.08 ^v/ 5.92 ^v

For ensureing that output triode does not end, answer > V _{t (max)}+ 0.2 ^v

$V_{W_1}>{6.08}^v/{5.92}^v+{0.2}^v={6.28}^v/{6.12}^v$

Still meet the demands when making load current maximal value 8.5mA × 2 (reverse signal), pull-up resistor R _lshould meet $8^v-8.5\mathrm{mA}\&times;2\&times;R_L>V_{W_1}={6.28}^v/{6.12}^v$

? $R_L<\frac{8^v-{6.28}^v/{6.12}^v}{17\mathrm{mA}}\&ap;101\mathrm{\&Omega;}/110.6\mathrm{\&Omega;}$

Desirable R _l(R12, R13) 100 Ω.

2.6 integration constant

Average (integration) capacitor C of output of U1 (AD834) _aVintegration constant Z with pull-up resistor formation ₁=R _lc _aVshould be greater than minimum incoming frequency (modulating frequency f _d) cycle (being less than 50us), at R _lwhen=100 Ω, C _aVshould be greater than desirable 1uF is also upper 0.1uF (filtering high frequency) again.

Therefore follow-up difference is counted amplifier can use intermediate frequency amplifier LF353 (10 ¹²Ω input impedance, 10 ⁵gain, 4MHz constant width (13) V/us Slew Rate); Owing to showing requirement>=100Hz (≤10ms), also can add one-level integration buffering, τ again ₂=47k Ω × 0.1uF=4.7ms.

2.7 additional triode Q ₁

Because second multiplier U2 is also that input impedance is lower (25K) also with AD834, feedback signal is taken from U ₀(output), thereby its load is heavier, adds one-level triode and increases output current, improves precision.

2.8 dynamic range

The input of this circuit, output amplitude and dynamic range are larger, but inner (differential voltage) signal is less, and this just requires the precision (resolution) of differential amplifier very high, tentative calculation once:

The maximum input current I of example _iwhen < 2A effective value, be transformed to voltage U _i=2 ^v, known by aforementioned transition function: $V_{W_1}-V_{W_1}=0.800\frac{{\left(V_i\right)}^2}{V^2}={0.206}^V.$

And input minimum current I _iwhen=10mA, be transformed to voltage U _i=10mV, known by aforementioned transition function: $V_{W_1}-V_{W_1}=0.800\&times;\frac{{\left(V_i^{\&prime;}\right)}^2}{V^2}=0.800\&times;\frac{{\left(2.5\mathrm{mv}\right)}^2}{V^2}\&ap;5.15\mathrm{uV}.$

Offset error impact will very large (W ₁=10K regulates), as being difficult to ensure precision under small-signal, can be to input signal stepping, but should note the peak factor problem (possible CF is larger) under little electric current when stepping, and must leave abundant allowance, give an example:

When points two grades taking 0.1A effective value electric current during as boundary line, input peak point current (Iip) should be got 0.6A above (CF > 6), AD834 input amplitude V ' _ipstill want < 1.5Vp, $U_{\mathrm{ip}}<1.5\mathrm{Vp}\&times;\frac{200\mathrm{\&Omega;}+{68\mathrm{\&Omega;}}^V}{68\mathrm{\&Omega;}}\&ap;5.9\mathrm{Vp}.$

In the time that transformer ratio is still 5, $\mathrm{Ro}=\frac{\mathrm{Uip}}{\mathrm{Iip}/5}<\frac{5.9\mathrm{vp}\&times;5}{0.6A}\&ap;49\mathrm{\&Omega;}.$

Example is got Ro=47 Ω, while inputting Ii=10mA, $U^{\&prime;}i=\frac{10\mathrm{mA}}{5}\&times;47\mathrm{\&Omega;}\&times;\frac{68\mathrm{\&Omega;}}{200\mathrm{\&Omega;}+68\mathrm{\&Omega;}}\&ap;23.85\mathrm{mV}.$

$\mathrm{UW}1-\mathrm{UW}2=0.800\&times;\frac{{\left(\mathrm{Ui}\right)}^2}{V^2}\&ap;0.455\mathrm{mV}$ Than single range

(Ro=5 Ω) increased approximately 90 times just more favourable to differential amplification.

Certainly while changing range, show and also must change, so that effective value is consistent (for example dwindles with input ).

3, CPU and display circuit:

Refer to Fig. 4, CPU is the C8051F350 chip of silicon company, and the internal oscillator frequency of this chip is 24.5MHz, comprises 16 ADC, and its AD resolution can reach 5uV in theory, is enough to meet accuracy requirement.For the intrinsic imbalance of the non-linear and circuit of some sampled point and the display error causing can proofread and correct by integrated method in software.AD conversion is carried out in CPU inside, ratio is calculated and proofreaied and correct, and output digit signals.

Display circuit is charactron.

Claims (4)

1. a metering circuit for high-frequency current, is characterized in that: described metering circuit comprises:

Sample circuit, is made up of Current Mutual Inductance coil and sampling resistor, and tested high-frequency current is become to sampled signal;

RMS-DC converter circuit, is connected with described sample circuit and receives described sampled signal, and this sampled signal is carried out to multiplying output effective value signal;

CPU, is connected with described RMS-DC converter circuit and receives described effective value signal, by this effective value signal through inner A/D change, ratio calculate and proofread and correct after output digit signals;

Display circuit, is connected with CPU and receives described digital signal, and this digital signal is shown.

2. the metering circuit of high-frequency current according to claim 1, it is characterized in that: described RMS-DC converter circuit is the negative-feedback circuit of the first multiplier, the second multiplier and differential amplifier composition, wherein, the first multiplier be input as described sampled signal, output is by the in-phase input end of integrating capacitor access differential amplifier, the input and output of the second multiplier connect respectively output terminal and the inverting input of differential amplifier, differential amplifier output effective value signal, this effective value signal is the root-mean-square value of the sampled signal of input.

3. the metering circuit of high-frequency current according to claim 1 and 2, is characterized in that: described sampled signal is high frequency low voltage signal, and described effective value signal is differential voltage direct current signal.

4. the metering circuit of high-frequency current according to claim 1 and 2, is characterized in that: the first described multiplier and the second multiplier are AD834, and described differential amplifier is LF353 intermediate frequency transport and placing device, and described CPU is C8051F350.