JPH0329714Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a highly sensitive balance stand for electronic balances.

<Prior art> Highly sensitive electronic balances with a reading limit of about 0.1 mg are sensitive to the movement of airflow that hits the weighing pan because of their high sensitivity. Therefore, all electronic balances in this class are equipped with a weighing chamber that is separated from the outside world by a windshield in order to prevent the wind from hitting the pan.
A weighing pan is placed in this weighing chamber. When loading and unloading samples on this plate, open the door provided in the weighing chamber.

<Problem that the invention aims to solve> By the way, electronic balances use electronic circuit parts such as ICs and transistors, and as is well known, these parts generate heat, and various measures have been taken to release this heat to the outside as much as possible. However, a certain amount of heat flows into the capacity chamber. Due to this inflow of heat, the temperature of the air in the capacity chamber increases, albeit slightly, and the air density decreases. When the door is opened to load and unload the sample onto the plate, convection as shown by the solid line in Figure 5 occurs due to the density difference with the outside air, and even after the door is closed, the same convection occurs for a specified period of time. Air flows, indicated by dashed lines in the figure, remain and each influence the dish 3. As a result, as shown by the solid line in the graph in Figure 6, the balance's indication changes not only from code a to b when the door is opened, but also from code b to c after the door is closed, and the indicated value changes immediately. is not stable. The time it takes for the indicated value to stabilize and reach the true value after the door is closed depends on the size of the dish 3 and the amount of temperature rise in the weighing chamber 1, but is approximately 10 to 10 minutes.
It takes 20 seconds. This time is a major factor in prolonging the measurement time.

For this reason, the conventional reading limit was 0.1 mg.
In the case of high-sensitivity electronic balances, the generation of heat and the addition of heat to the weighing chamber have been tried to be avoided as much as possible.

The purpose of this invention is to prevent the generation of convection due to the opening and closing of the door of the weighing room, and to prevent the generation of convection by opening and closing the door of the weighing room. To provide a balance stand for an electronic balance capable of shortening the time until the indicated value shows the true value after closing.

<Means for solving the problems> This will be explained using the embodiment drawings FIGS. 1 to 4. That is, the balance stand for electronic balances of the present invention is a balance stand 6 on which an electronic balance 20 with a weighing pan 3 disposed in a weighing chamber 1 having a door 2 that can be opened and closed is placed. A heating element 5 having a length approximately equal to the opening width w of the door 2 is provided via a heat insulator 4 at a position outside and below the door 2 of the electronic balance placed therein. It is something to do.

<Function> By setting the electronic balance on the balance stand 6 which has a heating element 5 installed at a predetermined position via the heat insulator 4, and heating the heating element 5 appropriately, there is no space outside the door 2. An upward airflow is generated as shown by the solid line in Figure 1. When the door 2 is opened in this state, there is almost no difference in density between the air inside the capacity chamber 1 and the air outside.
Electronic balance 20 of FIG. 5 in which heating element 5 is not used
Convection due to the inflow of outside air and the outflow of indoor air as in the case of 1 is unlikely to occur, and even if a small amount of air enters and exits, as long as the density remains the same, movement within the capacity chamber 1 is small. Furthermore, even if a downward airflow occurs in the capacity chamber 1 as shown by the broken line in FIG. 1 due to the generation of a slight convection at the moment when the door 2 is closed, it is canceled out by an approximately equal amount of upward airflow. After the door 2 is closed, rotational flow is less likely to occur in the capacity chamber 1.
A state of quiescence quickly appears.

<Example> Embodiments of the present invention will be described based on the drawings.

FIG. 1 is a partially sectional front view of a balance stand showing an embodiment of the present invention, showing a state in which an electronic balance is mounted. FIG. 2 is a perspective view of the main parts of the balance table.

In the electronic balance 20, a weighing chamber 1 is formed within a door 2, and a weighing pan 3 is provided within the weighing chamber 1. Such an electronic balance 20 is a typical example of a highly sensitive electronic balance. In contrast to this electronic balance 20, the balance stand 6 according to the present invention has the following features on its upper surface:
A heating element 5 is provided at a position outside and below the door 2 of the balance 20. This heating element 5 has a length approximately equal to the opening width w of the door 2 of the electronic balance 20 on which it is placed, and is provided via a heat insulator 4 so as not to directly heat the balance table 6. In the embodiment shown in FIGS. 1 and 2, the heating element 5 is embedded in the upper surface of the balance table 6.
Note that the heating element 5 is located on the left and right doors 2 of the electronic balance 20,
They may be provided for each door 2, or may be provided only for the door 2 that is used all the time.

FIG. 3 is a front view of the main parts of a balance table showing another embodiment of the present invention. In this example, instead of embedding the heating element in the upper surface of the balance table, a heating element 5 is provided in a protruding manner on the upper surface of the balance table 6 via a heat insulator 4. The heating element 5 is located at the door 2 of the balance 20.
It is similar to the previously described embodiments in that the area is located outside of and below.

FIG. 4 is a partially sectional front view of a main part of a balance table showing still another embodiment. The balance stand 6 shown in this example is a balance stand designed to prevent external vibrations from being transmitted to the balance, and a stand 7 that also serves as a weight is placed on a base 11 via a frame 9 and vibration-proofing rubber 8. The heating element 5 is provided in a part of the frame 9 via the heat insulator 4 so as to be located outside and below the door 2 of the electronic balance. The air heated by the heating element 5 rises and cold air enters through the gap 10. In addition, as a method to prevent external vibrations from being transmitted to the balance,
The balance 2 of the balance stand 6 shown in FIGS. 1 and 3 above
The upper surface portion on which the 0 is placed may be made to float with rubber.

In the above description, the heating element 5 may be composed of a sheathed heater, a film heater, or a semiconductor or ceramic heater in addition to a nichrome wire or the like.

Furthermore, the surface temperature of the heating element 5 will vary depending on the temperature rise in the weighing chamber 1 of the electronic balance 20 combined with the balance table 6;
It is better to set the temperature higher than room temperature by 0.5°C to 20°C. Therefore, the amount of heat generated by the heating element 5 can be set within a range of, for example, 0.1 W to 20 W, and the amount of heat generated can be variably adjusted.

Now, the electronic balance 20 is connected to the balance stand 6 according to the present invention.
When the heating element 5 is heated, an upward airflow is generated along the door 2, as shown in FIG. The degree of heating of the heating element 5 is determined in advance so that the air temperature within the airflow at this time is approximately equal to the air temperature within the capacity chamber 1. This eliminates the density difference between the inside and outside air, and even if the door 2 is opened, there is almost no air going in and out between the capacity chamber 1 and the outside. Therefore, when the door 2 is closed, rotational flow as shown by the broken line in FIG. 5 is unlikely to occur inside the weighing chamber 1 as in the conventional case, and even if a small amount of air enters and exits, as shown by the broken line in FIG. Even if a downward airflow occurs along the inner edge of the door 2, it is canceled by an upward airflow caused by heating of the heating element 5 that enters the capacity chamber 1 just before the door 2 is closed. As a result, the true value stabilized after the door 2 was closed, as shown in the graph in Figure 6, which shows the temporal change in the balance reading due to the opening and closing of the door 2, in comparison with the case where the heating element 5 is not attached. The time it takes to reach point c' shown in Figure 1 is 1/2 to 1/3 of the conventional time.

<Effects> The present invention has the above-mentioned configuration, and is used as a balance stand for an electronic balance.A balance stand with a length approximately equal to the opening width of the door is placed at a position outside and below the door of the electronic balance on which the electronic balance is placed. The heating element is installed through a heat insulator, which prevents air from entering and exiting the weighing chamber when the door of the electronic balance is opened, and also prevents air from flowing inside the weighing chamber when the door is closed. By suppressing this, it is possible to significantly shorten the time from when the door is closed until the weighing instruction value becomes stable and shows the true value. Therefore, the efficiency of weighing work can be improved. In addition, since less air enters and exits the weighing chamber when the door is opened, the indicated value will not deviate significantly from the true value when the door is open, making it effective even when weighing a certain amount, for example. It can be done.

[Brief explanation of drawings]

FIG. 1 is a partially sectional front view of a balance stand showing an embodiment of the present invention, showing a state in which an electronic balance is mounted. Figure 2 is a perspective view of the main parts of the balance table, Figures 3 and 4 are front views of the main parts of the balance table showing other embodiments of the present invention, and Figure 5 is a conventional example in which no heating element is provided. Figure 6 is an explanatory diagram of air flow in an electronic balance when a balance head is used. It is a graph showing temporal changes in indicated values as the door of the electronic balance is opened and closed. 1...Weighing room, 2...Door, 3...Dish, 4...
...Insulating material, 5...Heating element, 6...Balance table, 20
...Electronic balance, w...door opening width.

Claims (1)

[Scope of utility model registration request] A balance stand on which an electronic balance is placed, in which a weighing pan is placed in a weighing chamber with a door that can be opened and closed, and the electronic balance is placed at a position outside and below the door of the electronic balance. A balance stand for an electronic balance, characterized in that a heating element having a length substantially equal to the opening width of the door is provided via a heat insulator.