JPS6322264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved zero return circuit for returning the needle of a crossed coil meter to zero.

In moving coil type meters, moving iron piece type meters, etc., the needle returns to zero by a spring installed inside the meter when the input signal disappears, but crossed coil type meters are not equipped with such a means. In order to return the needle to zero, it is necessary to send a signal from outside the meter to return the needle to zero.

Figure 1 is a circuit diagram showing the configuration of a circuit that sends this type of signal, where 1 is the converter body that converts the digital signal input to the signal input terminal 2, the pulse frequency, etc. into analog voltage, and 3 is the resistor. 7, a drive circuit that converts the voltage output from the smoothing circuit into a signal for driving the meter 8; 9; is capacitor 10,
A backup circuit consisting of a diode 11, 12
is a switch, and 13 is a power supply. Here, in the smoothing circuit 3, the resistance values of the resistors 4 and 5 are each selected to be large in order to increase the time constant related to charging and discharging the capacitor 6.

In the conventional example configured as above, when the signal under test is input to the signal input terminal 2,
The signal is converted into an analog voltage by the converter body 1, smoothed by the smoothing circuit 3, and converted by the drive circuit 7 into a signal for driving the meter 8, which is then output to the meter 8. Then, the needle of the meter 8 indicates a value corresponding to the drive signal. In such a state, the capacitor 6 in the smoothing circuit 3 stores such charge that the voltage across the capacitor 6 becomes equal to the analog voltage output from the converter main body 1.

Next, when the switch 12 is opened in the above state, the signal from the signal source (not shown) is no longer input to the signal input terminal 2, and the capacitor 6 is connected to the resistor 5.
begins to discharge through. Therefore, the voltage input to the drive circuit 7 gradually decreases, and the driving signal for the meter 8 also decreases accordingly, so that the needle of the meter 8 returns to zero. In this way, until the needle returns to zero, that is, until the capacitor 6 finishes discharging, the capacitor 10 in the backup circuit 9 supplies voltage to the drive circuit so that the drive circuit operates.

However, in the above conventional example, since the resistance value of the resistor 5 is large (the time constant is large),
There were disadvantages in that the discharge time of the capacitor 6 became longer and the capacitance of the capacitor 10 had to be increased (several F).

Here, as a method of returning the needle of the meter 8 to zero, it is possible to cut the input signal before opening the switch 12 without providing the backup circuit 9 as shown in FIG. 1, but this method However, the disadvantage is that the needle suddenly returns to zero and bounces back again.

In order to solve the above-mentioned drawbacks of the conventional example, the present invention provides a discharge circuit for returning to zero that operates when the power is turned off, thereby making it possible to quickly return the meter needle to zero after the power is turned off. The present invention provides a zero return circuit that can reduce the capacitance of a capacitor in a backup circuit. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of an embodiment of the present invention, in which the same reference numerals as in FIG. A resistor 15 is used to determine a constant; 15 is a transistor that operates as a switch to discharge the charge stored in the capacitor 6 through the resistor 14 when the needle is returned to zero; 16 is a transistor that operates when the switch 12 is opened; This is a detection circuit that outputs a signal that keeps the transistor 15 in a conductive state after detecting this until the discharge of the capacitor 6 is completed.

In this embodiment configured as above,
When a signal is input to the signal input terminal 2, the signal is converted into an analog voltage by the converter body 1, smoothed by the smoothing circuit 3, and converted by the drive circuit 7 into a signal for driving the meter 8, which is output to the meter 8. be done.
Then, the needle of the meter 8 indicates a value according to the drive signal. In such a state, the capacitor 6 in the smoothing circuit 3 stores such charge that the voltage across the capacitor 6 becomes equal to the analog voltage output from the converter main body 1. Furthermore, since the detection circuit 16 outputs an "L" level signal to the transistor 15, the transistor 15 is in a non-conductive state.

Next, when the switch 12 is opened in the above state, the detection circuit 16 detects this and outputs an "H" level signal to the transistor 15, so the transistor 15 becomes conductive and the resistor 5 and Capacitor 6 begins discharging via 14. Therefore, the voltage input to the drive circuit 7 quickly drops, and the driving signal for the meter 8 also drops accordingly.
The needle of the meter 8 quickly returns to zero. Here, the value of the resistor 14 is selected so that the needle quickly returns to zero (the voltage across the capacitor 6 quickly becomes 0 (V)), so even after the power is turned off, The time it takes for the discharge to end is significantly shorter than in the past. Accordingly, the time for operating the drive circuit 7 and the detection circuit becomes shorter, and the capacitance of the capacitor 10 in the backup circuit 9 can also be made smaller than in the prior art.

As explained above, according to the present invention, when the power supply is connected, the time constant determined by the resistors 4 and 5 and the capacitor 6 in FIG. 2 is sufficiently large to eliminate ripples in the input signal. When the power is off, the mechanical moment of inertia of the meter needle can be taken into consideration, and the time constant can be switched to the one that will allow the needle to return to zero as smoothly and quickly as possible, and the capacitance of the capacitor in the backup circuit can be changed. It has the advantage of being smaller than conventional methods.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the configuration of a conventional zero return circuit.
FIG. 2 is a circuit diagram showing the configuration of an embodiment of the present invention. 1...Converter body, 2...Signal input terminal, 3...
...Smoothing circuit, 4,5,14...Resistor, 6,10
... Capacitor, 7 ... Drive circuit, 8 ... Meter, 9 ... Backup circuit, 11 ... Diode, 12 ... Switch, 13 ... Power supply, 15 ...
Transistor, 16...detection circuit.

Claims (1)

[Scope of Claims] 1. A converter that converts a signal to be measured into an analog voltage, a smoothing circuit that includes a capacitor and a resistor and smoothes the analog voltage, and an output signal from the smoothing circuit that is used to drive a meter. A meter drive circuit includes a drive circuit that converts the signal into a signal and outputs it to the meter, a detection circuit that detects that the power of the converter and the drive circuit is turned off, and a signal that is output to the capacitor by the output signal of the detection circuit. a discharge circuit configured of a resistor and a semiconductor switch element that discharges stored charge at a predetermined time constant; and a discharge circuit configured to operate the converter and the drive circuit from the time the power supply is turned off until the discharge ends. and a backup circuit for supplying voltage to the detection circuit, and the zero return circuit is characterized in that the needle of the meter is quickly returned to zero after the power is turned off.