PRECISION BALANCE OR MASS COMPARATOR WITH MODULE FOR DETECTING A MEASUREMENT UNCERTAINTY

Abstract

A precision balance including a weighing chamber (16), a draft shield (18, 20, 22) which surrounds the weighing chamber, a climate module (34) which is detachably disposed in the weighing chamber, a processor (32), a data input unit, and a data transmission path over which data is exchanged between the climate module and the processor. The processor has a measurement uncertainty determining module (33) with which the measurement uncertainty of the balance is determined. Also disclosed are a method for determining a measurement uncertainty of a balance and a climate module 4 that forms a self-contained modular unit, and includes an air pressure sensor (62), an air humidity sensor (54) and an air temperature sensor (52). A data transmission path transmits data to a processor external to the climate module.

Claims

1. Precision balance, comprising: a weighing chamber, a draft shield which surrounds the weighing chamber, a climate module which comprises an air pressure sensor, an air humidity sensor and an air temperature sensor, and which is detachably disposed in the weighing chamber and is configured to mount within an to detach from the weighing chamber, a processor, a data input unit, and a data transmission path over which data is exchanged between the climate module and the processor, wherein the processor comprises a measurement uncertainty determining module with which a measurement uncertainty of the balance is determined.

2. The precision balance as claimed in claim 1, wherein the data transmission path comprises an electrical plug-in connection or a wireless transmission path.

3. The precision balance as claimed in claim 1, further comprising a sensor coupled to the data transmission path and configured to determine a degree of ionization in the weighing chamber.

4. The precision balance as claimed in claim 1, wherein the weighing chamber comprises a light sensor, which is coupled to the data transmission path.

5. The precision balance as claimed in claim 1, wherein the processor is programmed to determine, based on a density of a substance to be weighed, an air buoyancy of at least a test sample or a buoyancy correction factor from the air pressure, the air humidity and the air temperature in the weighing chamber.

6. The precision balance as claimed in claim 1, wherein the measurement uncertainty determining module comprises a memory that stores results of earlier determinations of the measurement uncertainty.

7. Method for determining the measurement uncertainty of a precision balance that comprises a weighing chamber, which is separated from a surrounding area by a draft shield and in which an air pressure sensor, an air humidity sensor and an air temperature sensor are disposed, wherein the sensors are coupled to a processor and wherein a test sample is weighed, said method comprising: determining the air pressure, the air humidity and the air temperature in the weighing chamber with the sensors; weighing the test sample; determining a standard uncertainty of the weighing of the test sample; determining a standard uncertainty of the mass of the test sample; and determining a total uncertainty of the mass determination.

8. The method as claimed in claim 7, further comprising weighing a reference weight in addition to the test sample.

9. The method as claimed in claim 7, wherein the determination of the total uncertainty comprises factoring in results of earlier determinations of the total uncertainty.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is an exploded view of a precision balance according to the invention,

[0028] FIG. 2 is a perspective view of a climate module according to the invention which can be used with the precision balance according to the invention,

[0029] FIG. 3 is a side view of the climate module of FIG. 2 without the outer housing,

[0030] FIG. 4 is a plan view of the climate module of FIG. 2, also without the outer housing,

[0031] FIG. 5 is a flow diagram which illustrates a method for operating the balance, and

[0032] FIG. 6 is a flow diagram which illustrates a method for determining the total uncertainty of a mass comparison in accordance with OIML R111-1 carried out with the balance.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a high-resolution electronic precision balance which in this exemplary embodiment enables mass comparisons in all the accuracy classes under OIML R111-1 and also according to ASTM E617-13.

[0034] The precision balance comprises a load cell 14 with a base 12. The load cell 14 also comprises a weighing chamber 16 which is provided by a draft shield with adjustable side walls 18, a front wall 20 and a rear wall 22. The weighing chamber 16 is separated from the surroundings by the draft shield. A balance dish 24 serves for placement of the sample to be weighed. These components together form a weighing module 10

[0035] An electronic evaluation system 26 configured herein as a separate part is electronically linked via a cable 28 to the load cell 14. A display unit 30 which is linked to the evaluation system 26 serves both as a display and also as a data input unit. While the electronic evaluation system 26 and the display 30 are embodied as components physically separated from the weighing module 10 in the illustrated embodiment, other embodiments can incorporate one or both of these components 26 and 30 into the weighing module 10.

[0036] Among other things, a processor 32 which receives data from the load cell 14 is accommodated in the electronic evaluation system 26.

[0037] Also provided in the electronic evaluation system 26 is a measurement uncertainty determination module 33 with which the measurement uncertainty of a current weighing process can be determined. Furthermore, a memory in which the total uncertainty of earlier weighing processes is stored is also integrated into the measurement uncertainty determining module 33.

[0038] Provided in the weighing chamber 16 is a climate module 34 which is configured as a structurally separate unit which can mechanically couple via a releasable plug connection to the rear wall 22 (that is, it is mounted to be non-destructively releasable), preferably without the aid of a tool.

[0039] For this purpose, the rear wall 22 has two slots 36 spaced from one another in which flexible locking hooks 38 (see also FIG. 2) lock onto the outer housing 40 of the climate module.

[0040] The climate module 34 is shown in detail in FIGS. 2 and 4.

[0041] The outer housing 40 has numerous openings 42 via which the interior of the outer housing 40 transitions into the weighing chamber 16 and is part of the weighing chamber 16 so that the climate in the interior of the weighing chamber 16 corresponds to that in the interior of the outer housing 40.

[0042] The climate module 34 is linked electronically via an electric plug connection to a corresponding plug receptacle 44 in the rear wall 22. The plug receptacle 44 is electrically linked to the processor 32. A plug 46 with contacts 48 on the climate module 34 is inserted into the plug receptacle 44. Thus the plug 46 forms a module-side part of the electrical plug connection.

[0043] As an alternative to an electric plug connection, a wireless transmission, for example, WLAN or Bluetooth, can be used.

[0044] The electrical plug connection (or the alternatively used wireless transmission) forms a data transmission path with which data can be transferred from the climate module 34 to the processor 32 and possibly back again.

[0045] The plug 46 is preferably a portion of a circuit board 50 on which a plurality of sensors are arranged for detecting the climate in the weighing chamber 16. Thus, an air temperature sensor 52, an air humidity sensor 54, a light sensor 56 arranged in the immediate vicinity of an opening 42 and a sensor 58 for detecting the degree of ionization in the weighing chamber 16 are provided on the circuit board 50, as well as an electronic memory 60. An air pressure sensor 62 is electrically and mechanically connected via a holder 64 to the circuit board 50.

[0046] A plurality of the sensors can also be grouped together into combined sensors.

[0047] A wall 66 closes the shell-like outer housing 40 so that the narrow, tongue-like portion of the circuit board 50 positioned to the right of the wall 66 in FIG. 4 is pluggable into the rear wall 22 and into the plug receptacle 44.

[0048] Each sensor is linked to the processor 32 through suitable contacts 48. The memory 60 is also linked to the processor 32.

[0049] When operated as a comparator balance, the balance functions according to the following method, described by reference to FIG. 5:

[0050] The density of the sample to be weighed (test weight, also referred to as test sample B, and reference weight A) is input into the comparator balance in steps 100 and 102, for example via the display unit 30 which simultaneously serves, with a touch screen, as a data input unit. Alternatively, the density of the sample to be weighed can be input in advance.

[0051] A sample to be weighed is placed on the balance dish 24 after pre-settable process steps, for example, firstly the reference weight A, subsequently the test sample B twice and finally the reference weight A again. This involves a comparison weighing (double substitution) from which in step 104, the display difference of the balance is given. Other sequence steps are also possible, for example, ABA rather than ABBA.

[0052] The air pressure, the air humidity and the air temperature are determined in step 106 via the sensors 62, 54 and 52 and the corresponding data are then passed on to the processor 32.

[0053] The air density is determined in the processor 32 in step 108. Using the input densities, in the processor the air buoyancy correction factor is determined in step 110 and/or the air buoyancy of the sample to be weighed is determined dependent on the air pressure, air humidity, air temperature and the density of the sample to be weighed and, in step 112, the conventional weighing result of the test sample, i.e. the mass of the test sample B corrected by its air buoyancy is determined and reproduced as a protocol in the display unit 30, wherein the conventional mass 114 of the reference weight is included in the determination of the conventional mass of the test sample.

[0054] Furthermore, calibration values and correction values that were stored in the climate module 34 during the calibration of the climate module 34 are stored in the memory 60.

[0055] This calibration takes place outside the comparator balance. For this purpose, the climate module 34 is simply unplugged from the weighing chamber 16 without a wire connection needing to be released. The climate module 34 is then sent to a suitable calibration center which places the number of the calibration certificate, i.e. the new calibration values, the calibration date, the name of the calibrating laboratory and handling technician and the calibration history, into the memory 60. These values are later read out by the application program when the climate module 34 is in the precision balance or comparator balance again and is used directly in the calculation.

[0056] The values of the light sensor 56 and of the sensor 58 for determining the degree of ionization in the weighing chamber 16 are also determined.

[0057] For example, if the incident light level is raised, a suitable signal is output to the display that, for example, the measurement is inaccurate due to increased exposure to light and therefore an altered temperature in the weighing chamber. Thus an output signal dependent on the incident light level is emitted by the processor.

[0058] As soon as the degree of ionization is too high, an ionization device which ionizes the air in the weighing chamber is activated and provides for discharging of the sample to be weighed, or a warning of excessive charging of the sample to be weighed is issued.

[0059] The memory 60 is preferably an EEPROM.

[0060] Furthermore, the connection between the climate module 34 and the rest of the precision balance or comparator balance is realized with an PC bus.

[0061] The climate module 34 can be connected via a USB adapter into which it is plugged, to a computer in order to calibrate the sensors 52 to 58 and 62 without the climate module 34 having to be connected to the weighing module 10.

[0062] The total uncertainty of the mass determination is determined in the following way (see also FIG. 6):

[0063] Firstly, the standard deviation s is determined from the results of the calibration cycles. This is compared with the averaged standard deviation sp as found from previous measurements. The standard deviation determined for these measurements is stored in a memory of the measurement uncertainty determining module 33. If the difference between the current standard deviation and the averaged standard deviation of the earlier measurements is greater than a value defined as reasonable, the current weighing procedure is terminated. Otherwise, the uncertainty of the type A weighing process is determined from the standard deviation.

[0064] The type B uncertainty of the air buoyancy correction ub is calculated from the uncertainties of the air density, the material density of the reference and the material density of the test sample. The values for the uncertainty of the air density are stored in the climate module 34, where they were stored during its calibration.

[0065] The type B uncertainty of the balance uba is calculated on the basis of the uncertainty due to the sensitivity of the balance uE, the uncertainty due to the display resolution of the balance ud, the uncertainty of the balance due to eccentric loading uE and the uncertainty of the balance due to magnetism uma.

[0066] From the values for the type B uncertainty of the air buoyancy correction and the type B uncertainty of the balance, from the type A uncertainty for the weighing process and additionally from the known uncertainty of the mass of the reference, the broader total uncertainty of the weighing process is calculated. The special advantage lies therein that this can be realized integrated within the balance by the measurement uncertainty determining module 33 to which merely information concerning the test sample and the reference used must be input. All the other data are either stored therein or are automatically requested, for example, by calling the uncertainty values stored in the climate module. This enables the relevant total uncertainty to be given automatically for a weighing process.

LIST OF REFERENCE NUMERALS AND CHARACTERS

[0067] 10 weighing module [0068] 12 base [0069] 14 load cell [0070] 16 weighing chamber [0071] 18 side wall [0072] 20 front wall [0073] 22 rear wall [0074] 24 balance dish [0075] 26 evaluation system [0076] 28 cable [0077] 30 display unit [0078] 32 processor [0079] 33 measurement uncertainty determining module [0080] 34 climate module [0081] 36 slots [0082] 38 locking hook [0083] 40 outer housing [0084] 42 openings [0085] 44 plug receptacle [0086] 46 plug [0087] 48 contacts [0088] 50 circuit board [0089] 52 air temperature sensor [0090] 54 air humidity sensor [0091] 56 light sensor [0092] 58 sensor [0093] 60 memory [0094] 62 air pressure sensor [0095] 64 holder [0096] 66wall [0097] 100 step [0098] 102 step [0099] 104 step [0100] 106 step [0101] 108 step [0102] 110 step [0103] 112 step [0104] 114 conventional mass of reference weight [0105] A reference weight [0106] B test sample