JPH09243552A - Control of temperature of flow cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change over the polarity of the current flowing to a Peltier element and to control the temp. of a flow cell by a single power supply by making applied voltage constant and changing over the input terminal of the Peltier element. SOLUTION: Switches S1 and S2, S3 and S4 connected in series are further connected in parallel. One input terminal (a) of a Peltier element 5 is connected to the contact of the switches S1, S2 and the outer input terminal (b) thereof is connected to the contact of the switches S3, S4. In this constitution, when the switches S1, S4 are turned on and the switches S2, S3 are turned off in such a state that constant potential difference V is applied across points C, D, the current flowing to the element 5 flows in the direction I1 of terminal (a) → terminal (b) and, when the switches S1, S4 are turned off and the switches S2, S3 are turned on, a current flows in a direction 1I2 of terminal (b) → terminal (a). By this constitution, a power supply of both positive and negative polaritiies is not required and, even in a single power supply, the polarity of the current to the element 5 can be changed over and the temp. of the flow cell can be controlled by the single power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for an apparatus using a Peltier element for temperature control of a flow cell.

[0002]

2. Description of the Related Art Conventionally, a Peltier element has been used for controlling the temperature of a flow cell, and heating and cooling are performed by switching the polarity of the current passed through the Peltier element. As shown in FIG. 5, the polarity of the current flowing through the Peltier element is such that a positive and negative current source is used, one terminal a of the Peltier element 5 is grounded, and the other terminal b is a transistor or the like. It was decided by selecting the polarity of.

[0003]

In such a temperature control method, a stable current source having positive and negative polarities is required, and the power source capacity is required to be the same as positive and negative.

It is an object of the present invention to provide a method for controlling the temperature of a flow cell with a single power source and reduce the number of power sources.

[0005]

According to the present invention, as shown in FIG. 2, switches S1 and S2 and S3 and S4 connected in series are further connected in parallel. One terminal a of the Peltier element 5 is connected to the contacts of S1 and S2, and the other terminal b
Is connected to the contacts of S3 and S4.

When a constant potential difference V is applied between points c and d, the current flowing through the Peltier element 5 flows in the direction of I _{1 under} the condition 1 shown in Table 1 and I _{2 under the} condition _2. Flowing in the direction of.

[0007]

[Table 1]

With the above structure, the polarity of the current flowing through the Peltier element can be switched even with a single power source.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows an embodiment in which the present invention is used for controlling the flow cell temperature of a photometer. Reference numeral 6 is a flow cell of the light intensity measuring optical unit, and a thermistor 8 is provided in the vicinity thereof, and is set so that the temperature of the flow cell 6 can be detected.

The thermistor 8 constitutes a bridge circuit with the resistors R1, R2 and R3, and the thermistor 8 and the resistor R3.
One end is grounded, and one ends of the resistors R1 and R2 are grounded via the Zener diode ZD1. As a result, the potential difference Vz of the bridge circuit is fixed to a constant voltage (for example, -8V). The thermistor 8 and the resistor R1 are input to the non-inverting input terminal of the amplifier A1 via the resistor, and the resistors R2 and R3 are input to the inverting input terminal of the amplifier A1. As a result, the temperature change of the flow cell 6 is converted into the voltage change of the output Vo ₁ of the amplifier A1.

The output Vo ₁ is connected to the inverting input terminal of the amplifier A2 and the inverting input terminal of the amplifier A3 via a resistor, and the output Vo ₂ of the triangular wave oscillation circuit 9 composed of the amplifiers A4 and A5 is also amplified. It is connected to the inverting input terminal of A2 and the inverting input terminal of the amplifier A3. The feedback resistor R4 of the amplifier A2 is connected to the inverting input terminal, and the feedback resistor R5 of the amplifier A3 is connected to the non-inverting input terminal. As a result, the output Vo ₁ is added to the triangular wave output Vo _2, and is converted into two types of outputs, that is, the inverted addition output Vo ₃ and the non-inversion addition output Vo ₄ .

The output Vo ₃ is connected to the bases of the NPN transistor Q1 and the PNP transistor Q2 via a resistor. The output Vo ₄ is connected to the bases of the NPN transistor Q3 and the PNP transistor Q4 via a resistor. The collectors of the transistors Q1 and Q3 are connected to the driving power source Vp of the Peltier element 5, and the emitters of the transistors Q2 and Q4 are grounded. The Peltier element 5 is connected between the emitter of the transistor Q1 and the collector of the transistor Q2 via the current controlling resistor R6.
The other terminal b of the Peltier element 4 is connected to one terminal a of the transistor Q3 and the emitter of the transistor Q3 and the collector of the transistor Q4.

As compared with FIG. 1, the temperature feedback signal from the flow cell 6 is realized by the thermistor 8 in FIG. 3, and the temperature control circuit 1 in FIG. 1 has amplifiers A1 and A in FIG.
2, a circuit including A3, A4, A5. The Peltier drive circuit in FIG. 1 has transistors Q1, Q2, Q.
It is realized by a circuit composed of 3, Q4 and a resistor R6.

Next, the operation of this embodiment will be described with reference to FIGS. When the temperature of the flow cell 6 is at the control temperature, that is, when the bridge circuit is in a balanced state, the differential output V
o ₁ becomes 0V. At this time, the output Vo ₃ becomes a value obtained by inverting and amplifying the triangular wave of the output Vo ₂ and Vo ₁ , as shown in 1) of FIG. Output Vo ₄
Also, as shown in 2) of FIG. 4, the outputs Vo ₂ and Vo ₁ are taken into the next stage as non-inverting addition amplified values.
When the output Vo ₃ has a positive value, the transistors Q1 and Q2 that take the output Vo ₃ into the base turn on the transistor Q1 and turn off the transistor Q2, as indicated by 3) and 4) in FIG. At this time, the output Vo ₄ has a positive value, so that the transistors Q3 and Q4 that take the output Vo ₄ into the base are as shown in 5) and 6) of FIG.
Is off and the transistor Q4 is on. As a result, the direction of the current flowing through the Peltier element 5 flows in the direction of I ₁ .
When the output Vo ₃ has a negative value, the transistors Q2 and Q3 are turned on and the transistors Q1 and Q4 are turned off, so that the direction of the current flowing through the Peltier element 5 flows in the direction of I ₂ .

When the temperature of the flow cell 6 is not at the control temperature, that is, when the bridge circuit is in a balanced state, the differential output V
o ₁ becomes a positive value or a negative value. When Vo ₁ is a positive value, the output Vo ₃ has a value shifted to the − side as shown in 7) of FIG. 4, and the output Vo ₄ has been shifted to the + side as shown in 8) of FIG. It becomes a value. Vo _{1 When} the value is negative, the output Vo ₃ becomes a value shifted to the + side as shown in 13) of FIG. 4, and the output Vo ₄ is shifted to the − side as shown in 14) of FIG. It becomes a value. As a result, the on-time and off-time of the transistor fluctuate, and the current flowing through the Peltier element 5 is proportionally controlled.

[0016]

According to the present invention, the voltage applied to the input terminal of the Peltier element is kept constant and the input terminal of the Peltier element is switched so that the polarity of the current flowing through the Peltier element can be switched. As a result, it is possible to switch the polarity of the current flowing through the Peltier element even with a single power supply without the need for a power supply with both positive and negative polarities as in the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing the present invention.

FIG. 2 is an explanatory diagram of means for solving the problems of the present invention.

FIG. 3 is a circuit diagram showing an embodiment.

FIG. 4 is a timing chart showing the operation of the embodiment.

FIG. 5 is a conventional circuit diagram.

[Explanation of symbols]

1 ... Bridge circuit, 2 ... Temperature control circuit, 3 ... Single output power supply, 4 ... Peltier drive circuit, 5 ... Peltier element, 6 ... Flow cell, 7 ... Sample, 8 ... Thermistor, 9 ... Photometric unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideaki Ogura 1040 Ichige, Ichima, Hitachinaka City, Ibaraki Prefecture, Hitachi Science Systems, Inc. (72) Tsuneo Shimazaki, 1040 Ichige, Ichige, Hitachinaka, Ibaraki Within Hitachi Science Systems

Claims (2)

[Claims] 1. A Peltier element for controlling the temperature of the flow cell and a Peltier element for controlling the temperature of the flow cell, and a forward and reverse current are passed through the Peltier element to control the temperature. In a photometer having a circuit, a flow cell temperature control method is characterized in that a single power source is used as a power source for driving the Peltier element. 2. The temperature control method according to claim 1, wherein a triangular wave is added to the temperature control circuit to provide proportional control near the control temperature.