JPS61262636A - Uv detector - Google Patents

Abstract

PURPOSE:To prolong the life of a lamp, by changing the discharge current of a lamp as a light source corresponding to the use sensitivity of an ultraviolet (UV) detector. CONSTITUTION:A lamp lighting circuit 12 is equipped with a constant current circuit 14 and a discharge current setting circuit 16. The circuit 14 receives set voltage from the circuit 16 at the discharge current setting terminal 18 thereof and the current flowing to a deuterium lamp 2 is detected by a current detecting resistor R1 and a constant current is supplied to the lamp 2 through a diode D so as to make the voltage drop Vr of the resistor R1 equal to set voltage. A discharge current set value by the circuit 16 is automatically changed with the range of a detection system changed over by a range change-over circuit 40. By this method, because the life of the lamp 2 is prolonged and the lamp current is made large only at the time of high sensitivity use, a current equal to or more than a rated current is caused to flow without shortening the life of the lamp to enable the use of a detector in a small noise level state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a UV (ultraviolet) detector used as a detector for high performance liquid chromatography.

(Prior Art) Currently, variable wavelength UV detectors are most widely used as detectors for high-performance liquid chromatographs.

Generally, a deuterium lamp is often used as a light source in this UV detector because it has a strong emission intensity in the ultraviolet region and is relatively stable. Also used are xenon lamps.

The lamp is normally lit using a constant current circuit so that the discharge is maintained at the rated current value of the lamp.

(Problems to be Solved by the Invention) These deuterium lamps and xenon lamps have a drawback that they have a short lifespan (defined as, for example, the time when the luminous intensity becomes less than 1/2 of its initial value).

A typical deuterium lamp has a lifespan of about 500 hours.

The present invention aims to extend the life of lamps used as light sources in UV detectors.

(Means for solving the problem) 'UV detectors in high performance liquid chromatographs are used with various sensitivities depending on the purpose of analysis. When using a UV detector with a lower sensitivity, the light source intensity may also be lower, so the lamp does not necessarily need to be discharged at the rated current. Therefore, the present invention extends the life of the lamp by changing the discharge current of the lamp according to the sensitivity of the UV detector used.

That is, the UV detector of the present invention will be explained with reference to FIG. 1 showing an embodiment. The lamp lighting circuit (12) includes a constant current circuit (1
4) and a discharge current setting circuit (16) that sets a discharge current value to this constant current circuit (14), and dynamically adjusts the current setting value by the discharge current setting circuit (16) according to the range of the detection system. It was designed to change it to .

(Example) FIG. 1 represents one embodiment.

2 is a deuterium lamp as a light source, and is equipped with an anode 4 and a filament cathode 6.

A high voltage circuit 8 that applies a high voltage when starting discharge is connected to the anode 4 of the deuterium lamp 2 via a switch S, and the anode 4 is also connected to a lamp that supplies a constant current after starting the discharge. A lighting circuit 12 is connected.

The lamp lighting circuit 12 includes a constant current circuit 14 and a discharge current setting circuit 16. A set voltage is applied from the discharge current setting circuit 16 to the discharge current setting terminal 18 of the constant current circuit 14, and the current flowing through the deuterium lamp 2 is detected by the current detection resistor R1, and the voltage drop Vr of the resistor R1 is determined. It is configured to supply a constant current to the deuterium lamp 2 via the diode D so as to be equal to the set voltage.

The discharge current setting circuit 16 is an inverting amplifier circuit using an amplifier 20, and a constant voltage -v1 and a variable voltage +v2 switched by a range switching circuit 40 of the detection system, which will be described later, are applied to its inverting input terminal. .

22 is a spectrometer, 24 is a UV detector cell, 30° is a light receiving element, and the light emitted from the deuterium lamp 2 is separated into spectra by the spectrometer 22, and separated into a sample side channel 26 and a reference side of the cell 24. The channels 28 and 28 are irradiated, and each channel 2
The transmitted light at 6 and 28 is detected by the respective light receiving elements 30 and 32.

34 and 36 are the output currents I of the light receiving elements 30 and 32, respectively.
This is an amplifier that amplifies s and rr. 38 is a mask 34
．． This is a logarithmic amplifier that calculates the absorbance Vo+ as KQog(Ir/Is) from the logarithmic value of the output current of No. 36. 40 is logarithmic amplifier 3
This is a range switching circuit that attenuates the signal from 8 and sends it to the recorder, and at the same time changes the +v2 voltage of the discharge current setting circuit 16 in the lamp lighting circuit 12.

Detection elements 30, 32, amplifiers 34, 36, logarithmic amplifier 3
8 and the range switching circuit 4o constitute a detection system.

Next, the operation of this embodiment will be explained.

In the deuterium lamp 2, when the power is turned on, the filament 6 is first heated, and when a high voltage is applied from the high voltage circuit 8 through the switch S, discharge starts. After the discharge is started, the constant current circuit 14 performs constant current control on the discharge current Id so that Vr always remains constant, matching the set voltage. The switch S is turned off after the discharge starts.

Output of amplifier 20 of discharge current setting circuit 16 (Vl-V2
) is the discharge current Id of the deuterium lamp 2 supplied to the discharge current setting terminal 18 of the constant current circuit 14, and the deuterium lamp 2 is lit at the rated current, where I d =a (V+ -V2) In this case, a voltage of +V+ is applied to the discharge current setting terminal 18, and the discharge current Id of the deuterium lamp 2 at this time is Id=αv1.At this time, +v2 of the discharge current setting circuit 16 is changed to Ov by the range switching circuit 40. has been done.

The relationship between the range of the detection system and +V2 of the discharge current setting circuit 16 is set, for example, as shown in the table below.

In this table, the unit of the range of the detection system is AUFS (absorbance full scale). The larger the AUFS value, the
Sensitivity decreases.

By setting as shown in this table, the range is 0.01
When AUFS +V2/IV11 is 0, Id=αVt
Therefore, the deuterium lamp 2 lights up at the rated current. As the range goes up, V2/IVI l increases and the discharge current Id of deuterium lamp 2 decreases until the range reaches 2.56.
At the time of AUFS, Id=0.6Xαv1, and the deuterium lamp 2 is lit at 60% of the rated current.

By changing +v2 at the same time as range switching in this manner, the deuterium lamp 2 can be lit with a large discharge current when the usage sensitivity is high, and with a small discharge current when the usage sensitivity is low. When used at a low sensitivity, the emission intensity of the single deuterium lamp 2 is reduced, which increases the noise level, but there is no problem because the sensitivity is low. Further, since the deuterium lamp 2 is a discharge tube, even when the current is changed, the luminous intensity is quickly stabilized at the current value.

Note that since the UV detector takes the ratio of the signal on the sample side and the signal on the reference side as shown in the figure, the detection sensitivity does not change even if the light source intensity changes.

In the above table, when the range is 2.56AUFS, V2
=0.41V+l, but this value of 0.4 may be any other value. The relationship between the range and +v2 can be changed to another one as long as +v2 increases as the range becomes larger and the sensitivity becomes lower.

Figure 2 shows the discharge current setting circuit 16 in the lamp lighting circuit 12.
This represents another example of . In the example of Fig. 1, +v2 was changed, whereas in the example of Fig. 2, relay Kl was changed by 2
．． By switching the resistors R3, R4, . . . between the power supply +V' and the inverting input terminal of the amplifier 20,
It is designed to switch between...

In this way, by using a relay, it becomes possible to easily change the discharge current from the outside. For example, this is advantageous when processing the output of the logarithmic amplifier 38 in conjunction with the range of the data processing device.

Further, in FIG. 1, by setting +V2 to a negative voltage, the discharge current can be made larger than the rated current. Particularly when used with high sensitivity, the S/N ratio can be improved by making the discharge current larger than the rated current.

Since the lamp is turned off by setting +V2 = l V ll, the lamp can be turned off automatically when unnecessary.

The present invention is applicable not only to the case of using a deuterium lamp but also to the case of using a xenon lamp.

(Effects of the Invention) According to the present invention, a UV detector having the following advantages can be realized.

(1) The life of a deuterium lamp can be extended without deteriorating the performance of the detector.

(2) To increase the lamp current only when using high sensitivity,
It is also possible to use the lamp in a state where the detected amount has a lower noise level by flowing more than the rated current without shortening the lamp life.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment, and FIG. 2 is a circuit diagram showing a discharge current setting circuit in another embodiment. 2... Deuterium lamp, 12... Lamp lighting circuit, 14... Constant current circuit, 16... Discharge current setting circuit, 22... ...Spectrometer. 24... Cell, 30.32... Light receiving element, 38... Logarithmic amplifier, 40... Range switching circuit.

Claims (1)

[Claims] (1) In a UV detector that separates light from a lamp and irradiates it onto a cell of a liquid chromatograph and detects the transmitted light with a detection system to determine absorbance, the lamp lighting circuit of the lamp detects the discharge current of the lamp. The device includes a constant current circuit for controlling, and a discharge current setting circuit for setting a discharge current value in the constant current circuit, and is configured to automatically change the current setting value by the discharge current setting circuit according to the range of the detection system. A UV detector characterized by: