JPS6318900Y2 - - Google Patents

Description

[Detailed description of the invention] This invention detects special light excited by a solution and analyzes solution components using a spectrophotometer that detects a blank value (a constant value determined by the type of solvent) using a pure solvent. This relates to a zero sampling (zero point movement setting) circuit etc. for subtracting from a measured value for a solution containing a solute.

Generally, in this kind of spectrophotometer, the light that passes through the sample solution is converted into an electric current by a phototube such as a photomultiplier tube, and then sent to a recording and display device via an amplifier. Of the two input terminals of this amplifier, the input terminal that is not connected to the phototube is connected to a constant voltage power supply (negative feedback) through a potentiometer to give a voltage corresponding to the blank value. If you do this, the blank value will be subtracted from the detection signal (measurement) value at the output of this amplifier, and even if the gain is switched in the subsequent stage, the gain will be the same as the value after subtracting the blank value. This is convenient because a linear relationship can be maintained between the concentration of the solution or the amount of excitation light, etc., and the value displayed by the voltage and current value.

However, the gain magnification has a wide range of 1 to 1000 times, so when using a potentiometer to set a blank value, when the gain magnification is at its highest, a slight change in the potentiometer can change the display device. The zero point shift was large and it was difficult to set the zero point clearly.

As a means to eliminate the difficulty of setting zero suppression based on manual operation of the potentiometer, a method has been proposed that uses the charging voltage of a capacitor inserted in the feedback circuit of the first amplifier. Although this method is extremely effective in facilitating zero suppression, it is inevitable that the capacitor will naturally discharge, the terminal voltage will gradually decrease, and the zero point will drift.

Particularly recently, in addition to detection and measurement of trace components in medical clinical testing, biochemistry, food industry, etc.,
In the field of inorganic chemistry, there is also a demand for highly sensitive ultra-trace analysis, but in this case, high sensitivity requires high gain magnification, and the difficulty of adjusting the blank value cannot be ignored.

In consideration of the above, this idea was made to store the voltage value in digital memory instead of storing electricity in a capacitor.This made it possible to adjust the blank value, which was extremely difficult with manual adjustment of the potentiometer. The spectrophotometer is equipped with a high-performance zero suppression circuit that automates and easily performs the blank adjustment, and once the blank adjustment is completed, the blank value is always removed even if the gain of the entire device is changed. The purpose of this invention is to provide a signal detection device for use in meters, etc.

That is, the output of the first amplifier is converted into a digital signal by an A/D converter, passed through a latch circuit, that is, sampled, and stored in a digital memory, and then the contents of the digital memory are converted into a digital signal. Then, automatically feed back to the negative input terminal of the first amplifier, and adjust the gain of the D/A converter so that the output of the first amplifier becomes zero when measuring the blank value. For example, after that, it becomes possible to accurately remove blanks even if the gain is changed.

Next, an embodiment of the present invention will be described. In FIG. 1, 1 is a detector (photoelectron tube or photomultiplier tube), 2 is a first amplifier, 3 is a D/A converter,
4 is a main amplifier (with gain switching), 5 is a push button switch for capacitor discharge, 6 is a push button switch for feedback connection, 7 is an A/D converter, 8 is a latch circuit, 9 is a digital memory (storage circuit), 10 is a capacitor, 11 is an A/D conversion start signal input terminal, 12 is a latch operation (sampling operation) signal input terminal,
13 is a read command signal input terminal to the digital memory, and 11, 12, and 13 are input terminals for a command signal to read into the digital memory.When a zero suppression (not shown) on the equipment panel is pressed,
This is a control terminal to which signals are sequentially input to switches 5 and 6 at appropriate timings by a control device (not shown).

Next, the operation of the embodiment of the present invention will be explained. When measuring a blank value, for example, when a push button switch labeled "Zero Suppression" installed on the instrument panel is pressed, switch 5 is closed (at this time switch 6 is open) and capacitor 10 is closed, as shown in FIG. Since the charges are short-circuited and the negative input terminal voltage of the first amplifier 2 becomes zero, the first amplifier output 2
increases to a value corresponding to the positive terminal input blank value. The output is converted into a digital signal by the A/D converter 7, passed through the latch circuit 8 (while the latch operation signal 12 is not input, the digital signal simply passes through the latch circuit 8), and is transferred to the digital memory. The stored contents of the digital memory 9 are then reconverted into analog signals by the D/A converter 3. At this time, when the switch 6 is closed and the switch 5 is opened, the analog output signal of the D/A converter 3 charges the capacitor 10 and is applied to the negative terminal of the first amplifier 2. In this state, the analog gain of the D/A converter 3 is adjusted so that the output of the first amplifier 2 becomes zero volts. Since the gain is latched and held constant, the gain can be easily adjusted. In addition,
The number of bits of the A/D converter 7 must be selected to be large enough to provide sufficient accuracy.

Therefore, since the stored value in the digital memory 9 does not change, as long as the blank value is constant,
It becomes possible to perform zero suppression very easily and to accurately remove blank values.

Note that a capacitor 10 is provided in parallel with the switch 5 that short-circuits the feedback terminal of the first amplifier to zero potential, but in a practical circuit, the presence of this capacitor 10 closes the switch 6. Switch 5 can be opened once the discharge of capacitor 10 is completed even if the switch 5 and 6
It is easy to time the opening and closing of the switch 6), and the sudden voltage fluctuation at the negative input terminal of the first amplifier when the switch 6 is closed is smoothed out.

As detailed above, when manually performing zero suppression using a potentiometer,
When the gain was at maximum, the potentiometer knob was very sensitive to adjust, making it difficult to set, but now that switch switching and digital circuit operation have been automated, setting errors have become extremely small.
Settings have become easier. Furthermore, since a zero suppression circuit is installed before the gain switching, the blank value can be accurately removed by just performing the blank adjustment once and even if the gain is switched thereafter. Although the above embodiments have been described for removing blank values, it is clear that the invention is not limited to this and can also be used for baseline correction, noise signal removal, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. 1: photomultiplier tube, 2: first amplifier, 3: D/A
A converter, 4: main amplifier, 7: A/D converter,
8: latch circuit, 9: digital memory, 1
0: capacitor, 11: A/D conversion start signal terminal, 12: latch command signal terminal, 13: digital memory read command signal terminal.

Claims (1)

[Scope of utility model registration request] In addition to the signal transmission system that amplifies the detection signal from the detector and records and displays it, there is an A/D for the signal component after amplification.
a conversion circuit, a storage circuit that samples and stores this digital signal, a latch circuit provided between this storage circuit and the A/D conversion circuit, and a D/A conversion circuit for the digital storage value;
A circuit that negatively feeds back the signal from this D/A conversion circuit to the amplifier via a feedback connection switch, a switch that short-circuits the feedback terminal of the amplifier to zero potential, and a circuit connected in parallel to this switch. A signal detection device characterized by comprising a feedback circuit consisting of a connected capacitor.