JPS6056010B2 - Recorder filter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input filter circuit for an unbalanced amplifier, and more particularly to a recorder filter circuit that functions as a filter without being affected by common mode voltage.

Figure 1 is a block diagram showing the principle of the recorder.
In the figure, 1 and 2 are input terminals of the recorder, 4 is a filter circuit, and 5 and 6 are output terminals of the filter circuit, and are also input terminals of an amplifier 7.

Reference numeral 8 denotes a servo motor, to which a recording pen 9 is attached, and furthermore, a slide resistor 11 is also interlocked.

The output of the slide resistor 11 is connected to an amplifier 7.
10 is a recording paper, 12 is a first line, and 13 is a second line.

In such a configuration, the recorder has a 50 or 60 H2
commercial frequency noise (in the case of DC voltage measurements, induced voltage from these power lines is considered a type of measurement interference noise), and high frequency noise such as TV radio waves, radio waves (carrier waves), transceiver radio waves, etc. invade.

As shown in FIG. 2, these noises enter the recorder in the form of common mode noise voltage ec, which enters as a voltage between the first and second lines 12 and 13 and the ground, and the first
There is a normal mode noise voltage en that enters as a voltage between the line 12 and the second line 13.

These may enter from the input terminal of the recorder, and sometimes from the power line (alternating current). In addition, in rare cases, common mode noise may enter through the capacitance of a transceiver or the like. Conventionally, as a filter circuit for removing noise, a low-pass filter shown in FIG. 2 has been used.

This filter circuit has a damping effect on the common mode voltage from the first line 12, but has no damping effect on the common mode voltage from the second line 13. Therefore, as shown in FIG. 3, there is a resistance R on the second line 13 side as well.

and capacitor C2, all the noise is caused by capacitor C2.
It is necessary to configure the circuit so that the current flows to the ground terminal side through the . In Fig. 3, the normal mode noise En is zero V.
Assuming that, the high frequency noise voltage E induced between the first and second lines 12, 13 and the ground by television radio waves, etc.

is on the order of 100 MHz, so it is a well-known fact that even a single wire of about 10 to 20 cm acts as L, that is, inductance, for this frequency component. Therefore, the first line 12 and the second line 13 act as the same inductor against high frequency noise. Noise currents Ic, , Ic2 generated by this noise voltage Ec act, and E
A voltage of cl, ec2 is generated. In this case, if the resistances R1 and R2 between both lines are equal, the norm mode noise voltage Δ■C will not occur between the output terminals 5 and 6. but,
If there is a slight resistance difference between both lines, a normal mode noise voltage ΔVc is generated between the output terminals 5 and 6. This conversion process is the common mode noise that appears between both lines and the ground due to the conversion of noise from common mode to normal mode (the common mode component itself has no adverse effect on the signal voltage, but If the conversion is performed, it will be superimposed on the signal voltage and cause problems)
This means that it has an adverse effect on the operation of the signal circuit.

The above conversion measures the DC:V signal like a recorder (
This is done in the circuit section where a maximum detection sensitivity of 1pV to 10μ is normally required. and seriously impair the measurement results.

There are two main obstacles: one is induction interference caused by TV radio waves and transceivers. A recorder (full span 1mv, sensitivity 1μV) installed near the window of a building several kilometers away from Tokyo Tower and directly visible to the tower detected vibrations from the pen. This can result in multiple recordings, and can also cause the pen indication to deviate by a few percent to several tens of percent of the full span.Furthermore, if a transceiver is used nearby, a phenomenon similar to that of television radio waves will occur each time a transceiver is used. As a result, there are countless examples of problems caused during maintenance of switchboards, etc. The other one is commercial frequency induction disturbance,
Particularly in the case of temperature measurement, where the distance between the detector and the recorder input terminal is more than 10 degrees, if there is a strong magnetic field nearby, an induced voltage will be generated between the lines and between the line and the earth (ground).
Normal mode and common mode), it has been reported for a long time that this induced voltage causes trouble in indicating and recording, and has received attention. In either case,
There is a possibility that conversion from common mode to normal mode will occur, but in the case of commercial frequencies, there is little impedance unbalance on the line side (because only the DC resistance component is effective due to the low frequency) and conversion to normal mode is possible. Even if there is a conversion of Therefore, the adverse effects on the recording operation (in severe cases, the pen may vibrate or the indication deviation may appear) can often be removed relatively easily. On the other hand, common mode noise that enters at high frequencies (TV radio waves, etc.) can easily turn a single wire into an inductance, making it difficult to perfectly balance the impedance between the wires.

In addition, the wiring route and wiring pattern (on the print board) of the first line 12 and the second line 13 can be wired at several tens of KHz to several tens of MHz.
Since it is virtually impossible to achieve complete matching over the Hz band, it is considered that impedance to high frequencies is unavoidable. As a countermeasure against high frequency noise such as from television radio waves, it is necessary to remove the high frequency noise before entering the amplifier. For this reason, it is very effective for removing common mode noise to insert an inductance L having a high high frequency removal effect in both lines as shown in FIG. 4 instead of the resistor shown in FIG.

However, if the signal line is grounded with a capacitor,
Due to the common mode noise voltage Ec'', common mode high frequency noise and commercial frequency noise current intrude through the stray and insulation resistance between the primary and secondary windings of the power transformer, and further through the rectifier 1 and the amplifier 7. It flows into the country.

By the way, terminals 1 and 2, which are the connection points with the signal line, are the terminals of the recorder, and generally the ground side of the signal source is connected to one side (terminal 2), so the common mode current Ic due to the common mode noise voltage @'' is not affected by this because it does not go through the signal source resistance Rs.However, the terminal 1 of the signal source
) is grounded, the common mode current 1c due to the common mode noise voltage Ec'' flows through the signal source resistance, so a normal mode noise voltage component Rs-1c is generated, causing noise disturbances. In order to minimize the amount of current flowing from the common mode voltage Ec'' between the curtain and the ground, it was necessary to improve the insulation of the power transformer and the like.
SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a filter circuit for a recorder that is not affected by the common mode voltage generated between the amplifier and the ground and has a remarkable noise removal effect.

Hereinafter, one embodiment of the present invention will be described based on the drawings. In FIG. 5, the first line 12 and the second line 13 are
An inductance L is inserted respectively, and the first line 12
A first capacitor C3 and a second capacitor C3 are connected between the
A second capacitor C4 and a third capacitor are connected between the line 13 and the ground.
A capacitor C5 is connected.

That is, the inductance L of the first line 12 and the first capacitor C3 form a low-pass filter circuit, and the inductance L of the second line 13, the second capacitor C4, and the third capacitor C5 form a π-type filter circuit. A low-pass filter circuit is configured. Therefore, most of the noise current 1C1 generated by the common mode insulation voltage Ec'' is removed by the capacitor C5, and by connecting the capacitor C3 between the first line 12 and the second line 13, the high frequency noise component is removed. On the other hand, since the connection point of the capacitor C3 is equivalently short-circuited and no longer flows through the signal source resistor R5, the signal voltage is not affected.

As a result, the allowable signal source resistance R5 can be increased, and the degree of utilization is increased. Note that it is even more effective to add a capacitor and a choke coil between the first line 12 and the second line 13 and between the second line 13 and the ground.

As described above, according to the present invention, it is possible to provide a recorder that has the same high frequency noise attenuation characteristics as the conventional recorder and is not affected by noise current.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the principle of a recorder, Figures 2 and 3 are diagrams showing a conventional filter circuit, Figure 4 is a block diagram showing a conventional recorder, and Figure 5 is a recorder according to the present invention. 4. Filter circuit, 7. Amplifier,
8... Servo motor, 9... Recording pen, 11... Slide resistor, 12... First line, 13... First line. 2 tracks.

Claims (1)

[Claims] 1 In a recorder in which a recording signal is input to an amplifier through a low-pass filter circuit, the output from the amplifier drives a servo motor and a slide resistor, and records with a recording pen. , the low-pass filter circuit,
a low-pass filter circuit comprising an inductance and a first capacitor provided between a first line and a second line; a second capacitor provided between the second line and the ground; 1. A filter circuit for a recorder, comprising a third capacitor and a π-type low-pass filter circuit comprising an inductance, the first capacitor and the second capacitor being electrically connected in series.