Article for the 29th Sensing ForumControl Method for Weighing Instruments Using theEnvironment Logger AD-1687

Presented by: Naoto Izumo, Masahiro Kanno, and Sachiko Shimizu
R&D Division 5, A&D Company, Limited
Organized by: The Society of Instrument and Control Engineers (SICE)

September 27 to 28, 2012
Hitachi Campus, Ibaraki University
Ibaraki, JAPANControl Method for Weighing Instruments Using the Environment Logger
AD-1687
Naoto Izumo, Masahiro Kanno, Sachiko Shimizu

A&D Company Limited

Higashi-Ikebukuro, Toshima-ku, Tokyo 170-0013 Japan
Abstract
We report on the error factors for weighing data which are caused by environmental factors andshow how to improve repeatability which is important for measurements with balances. Data used
was taken by the environment logger AD-1687 over a long duration. We also report analysis
examples which improve repeatability.
Keywords
Analytical balance, Environmental error factor, AND-MEET

1) Introduction
Many electronic balances are used in laboratories and quality control fields. Presently,
high-sensitivity analytical micro balances are available on the market which can display
measurements as small as 1/100th of the weight of a 1 yen coin (1µg or mcg). The resolution
capability of these electronic balances reaches 1 in 20 million parts of the maximum
measureable load. Due to the high resolution and microscopic display capabilities, changes in
the immediate environment of balances can lead to instability in measurements. *1 It istherefore regarded as essential to assess the installation environment of analytical balanceswith specialized tools in response to the many problems that can occur with such highresolution instruments. In order to resolve this potential problem we have recently developed
the Weighing Environment Logger AD-1687*２
The AD-1687 detects not only temperature, humidity and atmospheric pressure, but also
the level of vibrations balances are subject to. If the optional water temperature sensor is used,
six different measurement parameters can be logged together in one reading (including theactual weight measurement). Further, timing of the measurements can be set freely by theuser at intervals of as small as one second apart, with all six parameters being logged as a
distinct measurement set. The AD-1687 can record up to 10,000 of these sets and display thismeasurement data in a time series graph. For example, by using this environment logger forcontinuous measurements of weight and environmental data over a 24 hour period, clear
judgment can be made on many environmental factors that are beyond normal humanperception, such as loss of stability and repeatability from people entering and leaving themeasurement room, the influence of the smallest earthquakes, the slightest fluctuations intemperature from automatic air conditioning control that would go unnoticed by staff andchanges in atmospheric pressure and humidity from outside weather. By confirming theseenvironmental influences the precise cause of any measurement instability can be properly
ascertained and measures to correct these influences can be performed.
The following cases present clearly identified environmental error factors that affectweighing results, based on data taken over a long time duration using the environment logger.
Moreover, concrete measures to improve the repeatability of balances with actual measurement
examples will also be reported.
2) Measuring environmental data
The specifications of the Weighing Environment Logger AD-1687 and the environment
measurement method using a microbalance are as follows: The AD-1687 is compact-size,
drip-proof (IP65) with a durable body for portable use and can withstand a fall of up to 1.5
meters. Also, since the humidity sensor is a disposable item, it is placed in a separate box withthe temperature sensor, which is then connected with the logger via a connector. This makes it
easy for the user to exchange the humidity sensor.
In tests of the AD-1687, BM-20 analytical balances with minimum measurement displayof 1µg were used. The BM-20 has a weighing capacity of 22g, hence a resolution capability of 1
part in 22 million. These balances and environmental loggers were set up next to each other as
in Fig. 1 and repeat measurements were conducted over a 24 hour period, automaticallymoving an embedded 20g weight up and down on the balances. An environmental logger wasconnected to each micro balance and while weight was being measured environmental data
was also recorded for temperature, humidity, atmospheric pressure and vibrations. The
AD-1687 unit can be seen in Fig. 2.

Fig.1 Alignment of balance andFig.2 AD-1687

weighing environment logger

The results of measurements over the 24 hour period are displayed in Fig. 3 for reference.
The cycle of up-down movement of the weight lasted 60 seconds and data was captured for bothfull load and zero balance every minute, resulting in 1440 data sets over the 24 hour period.
The difference of span between full load and zero balance was measured and repeatability(standard deviation) was calculated for every 10 neighboring span values. Each repeatability
value was then plotted as a dot and connected by a zigzagged line as shown in the graph below.
The x-axis measures the time scale over the 24 hour period, the left y-axis measuresrepeatability in 1µg units and the right y-axis measures the change in room temperature where
the weighing measurements took place.
This data was obtained from a test conducted at our company’s main point of production,
our factory in Tsukuba, Japan.

Throughout the 24 hour period, an average repeatability of

1.3µg was maintained, easily meeting the catalog specification criteria of the BM-20 of 2.5µg
for 1g of weight. Over this 24 hour period room temperature was found to vary byapproximately 2°C, and although not represented on the graph, humidity varied by 4% andatmospheric pressure by 3 hPa. The data indicates that as the number of people who wereallowed to enter the room was limited, under these environmental conditions even without anexternal tabletop breeze break or anti-vibration table the basic performance of the
microbalance could be maintained for 24 hours. The evaluation method for relating
measurement repeatability to environmental error factors has already been established as“AND-MEET” *3 and is conducted at various locations of use of a balance in response to users’
requirements.

BM-20(T1000401) 製造時
繰り返し性(標準偏差)[ug]BM20スペック(1g)

温度[℃]

20.0

30
繰り返し性(標準偏差)平均 1.3 [ug]

14.0

27

12.0

26

温度( 右軸)

10.0

25

8.0

24

6.0

繰り返し性( 左軸)23

B M2 0 ス ペック( 1 g)

Fig.3

Example of weighing environment measurement

3) Measurement results
From the results displayed in Fig.3 it was
confirmed that the microbalance performed withgood repeatability under an ideally equipped

11/6/22
14:00

11/6/22
11:00

20
11/6/228:00

0.0
11/6/225:00

21
11/6/222:00

2.0
11/6/2123:00

22

11/6/21
20:00

4.0

温度[℃]

28

11/6/21
17:00

日付
時刻

29

16.0

11/6/2114:00

繰り返し性(標準偏差)[ug]

18.0environment,

requiringneitheranexternal

tabletop breeze break nor an anti-vibration table.
However, it was still necessary to confirm the effect
such

items

may

have

in

reducing

external

disturbances in measuring environments wherethese occur regularly.
Therefore, to try and replicate the type ofenvironment

in

the

field

where

external

disturbances are frequent we selected the 2nd floor
scale verification room in our R&D Center in
Kitamoto, Saitama, Japan. In our scale verification
room there are many people coming or going toinspect weighing scales, 20kg weights being loaded
or unloaded, doors being open and closed and many
disturbances of air by people moving around theroom or from the air con unit. The arrangement of

Fig.4 Scale verification room

equipment for this test in our scale verification
room can be seen in Fig. 4. In the photo you can see
two high-capacity industrial balances performing
measurements for verification. In front of themalongside the wall you can see two analyticalbalances taking data for this experiment.
① Influence of air conditioning or people’s movement and effect of anti-vibration table andtabletop breeze break (Fig.5 & 6)
The results of the test for repeatability conducted on August 10 (Friday) this year from 3
pm until 3 pm the following day are displayed in the graphs in Fig. 5. Fig. 5-1 shows results
where the anti-vibration table and tabletop breeze break were used, Fig. 5-2 shows the results
where they were not. Until Friday evening, when many people were still working in theverification room the repeatability results for both tests were bad and large differences can beseen in the values. Further, after the busy Friday evening period the graph on the left showsthat repeatability fell below 2.5µg, within the catalog specifications for the standard deviation
for repeatability (σn-1). However, the graph on the right shows a worsening of repeatability,
exceeding the specifications on several occasions.

36
35

繰り返し性(標準偏差) [ug]BM-20 1g スペック
温度 [C]
20.0
繰り返し性(標準偏差)平均 2.4 [ug] ※地震等突発の外乱を除く
18.0

16.0

34

16.0

34

14.0

33

14.0

33

12.0

32

8.0

30

6.0

29

繰り返し性

4.0

28

12.0

36
35

32

温度

10.0

31

8.0

30

6.0

29

繰り返し性

4.0

28

12/08/11
1 5 :0 0

12/08/11
1 2 :0 0

12/08/11
0 9 :0 0

12/08/11
0 6 :0 0

12/08/11
0 3 :0 0

12/08/11
0 0 :0 0

12/08/10
2 1 :0 0

12/08/10
1 8 :0 0

日付
時刻

12/08/10
1 5 :0 0

12/08/11
1 5 :0 0

12/08/11
1 2 :0 026

12/08/11
0 9 :0 0

0.0

12/08/11
0 6 :0 026
12/08/11
0 3 :0 027

0.0
12/08/11
0 0 :0 0

2.0

12/08/10
2 1 :0 027
12/08/10
1 8 :0 0

2.0

日付
時刻

温 度 [C ]31

繰 り 返 し 性 ( 標 準 偏 差 ) [u g ]BM20 FE検査室 除振台無 卓上風防無 2012.08.10-08.11

温 度 [C ]温度

10.0

12/08/10
1 5 :0 0

繰 り 返 し 性 ( 標 準 偏 差 ) [u g ]BM20 FE検査室 除振台有 卓上風防有 2012.08.10-08.11 パッシブ除振台
繰り返し性(標準偏差) [ug]BM-20 1g スペック
温度 [C]
20.0
繰り返し性(標準偏差)平均 1.7 [ug] ※地震等突発の外乱を除く
18.0

Fig.5-1 With anti-vibration table andFig.5-2 Without anti-vibration table

tabletop breeze break

and tabletop breeze breakIn this test, room temperature, humidity and vibration data were simultaneously recordedby the environmental logger and are displayed in the graph in Fig. 6. This graph shows thatover a 24 hour period room temperature changed just less than 4°C, humidity varied by amaximum 10% and vibration force was within 2-5 Gal. It also shows that until Friday evening
when the worsening of repeatability was observed, there were humidity changes of 10%/30
minutes accompanied by minute fluctuations in room temperature, which was probably causedby the air conditioning.
温度
湿度
振動

Max: 34.5C Min: 26.5C
Max: 62.8% Min: 45.3%
Max: 738Gal Min: 3Gal

パッシブ除振台

AD1687 FE検査室 除振台有 卓上風防有 2012.08.10-08.11
温度

振動

28
湿度

24
20

40

16

温度

30

12

20

8

振動

12/08/11
15:00

12/08/11
12:00

12/08/11
09:00

0
12/08/11
06:00

0
12/08/11
03:00

4
12/08/1100:00

10
12/08/10
21:00

振動 [Gal]50

12/08/10
18:00

日付
時刻

湿度

60

12/08/10
15:00

温度 [℃] / 湿度 [%]70

Fig. 6 Environmental logger data (temperature, humidity, vibrations)

From Fig. 5 & 6 we can determine that adverse effects from vibrations generated by the
movement of people or from air movement from air conditioning can be mitigated by the use oftabletop breeze break and anti-vibration table, which can improve repeatability at themicrogram level. Even after the effects of people’s movement or air conditioning had ended
after Friday evening, and also when experiencing non-controlled natural temperature changes,
environmental error factors can be reduced by the use of tabletop breeze break or
anti-vibration table. In this test, they led to a reduction of repeatability from a 2.4µg average to
1.7µg, a small but clear improvement.
② Influence of earthquakes (Fig. 7 & 8)
The metric structure of electromagnetic equilibrium balances is the same as that of highprecision seismographs. Therefore, the reaction of these to earthquakes is extremely sensitive.
Judging from their resolution capabilities, analytical balances should actually have a higher
level of sensitivity than seismographs.
Data from the time of an actual earthquake is displayed in Fig. 7. The graph is a record of
repeatability of weight measurements and room temperature from 3pm on July 2 (Monday)
until 3 pm the following day. On July 3 (Tuesday) at 11:31am there was an earthquake inTokyo Bay of Magnitude 5.4, or Level 4 on the Japanese seismic intensity scale. Shaking was
also confirmed at the testing location. At that point in time, the repeatability of the balancesslipped significantly, from a prior average of 2µg to a sudden increase to 20µg. Fig. 7-1 shows
measurements performed with an anti-vibration table; Fig. 7-2 performed without one. Further
data from the environmental logger is displayed in Fig. 8, where 14 Gal vibrations were

Fig.７-１ With anti-vibration table

35
34
33
32
31
30
29
28
27
26
25
24
23
22
12/07/03
1 8 :0 0

12/07/03
1 5 :0 0

12/07/03
1 2 :0 0

12/07/03
0 9 :0 0

12/07/03
0 6 :0 0

12/07/03
0 3 :0 0

12/07/03
0 0 :0 0

12/07/02
2 1 :0 0

日付
時刻

12/07/02
1 8 :0 0

繰 り 返 し 性 ( 標 準 偏 差 ) [u g ]BM20 FE室 除振台無 2012.07.02-07.03
繰り返し性(標準偏差) [ug]BM-20 1g スペック
温度 [C]
26.0
繰り返し性(標準偏差)平均 3.4 [ug] ※地震等突発の外乱を除く
24.0
22.0
20.0
18.0
16.0
14.0
温度
12.0
10.0
8.0
6.0
繰り返し性
4.0
2.0
0.0
12/07/02
1 5 :0 0

35
34
33
32
31
30
29
28
27
26
25
24
23
22
12/07/03
1 8 :0 0

温度 [C]

12/07/03
1 5 :0 0

12/07/03
1 2 :0 0

12/07/03
0 9 :0 0

12/07/03
0 6 :0 0

12/07/03
0 3 :0 0

12/07/03
0 0 :0 0

12/07/02
2 1 :0 0

日付
時刻

12/07/02
1 8 :0 0

26.0
繰り返し性(標準偏差)平均 2.3 [ug] ※地震等突発の外乱を除く
24.0
22.0
20.0
18.0
16.0
14.0
温度
12.0
10.0
8.0
6.0
繰り返し性
4.0
2.0
0.0
12/07/02
1 5 :0 0

繰 り 返 し 性 ( 標 準 偏 差 ) [u g ]BM-20 1g スペック

温 度 [C ]BM20 FE室 除振台有 2012.07.02-07.03
繰り返し性(標準偏差) [ug]

温 度 [C ]detected from the earthquake (equivalent to about Level 3 in seismic intensity).

Fig.７-2 Without anit-vibration table

From Fig. 7 it can be seen that while an anti-vibration table can stabilize measurement
values under normal conditions, with respect to large low-frequency shaking such as anearthquake it is quite ineffective and the balances have no ability to record reliable data.

Max: 27.6C Min: 24.3C
Max: 60.6% Min: 51.8%
温度
湿度
Max: 1244Gal Min: 3Gal
AD1687 FE室 除振台無 2012.07.02-07.03

振動

35
湿度

60

30

50

25

40

20
温度

30
20

15
10

振動

Fig.8

12/07/03
18:00

12/07/03
15:00

12/07/03
12:00

12/07/03
09:00

12/07/03
06:00

日付
時刻

12/07/03
03:00

0
12/07/03
00:00

0
12/07/02
21:00

5
12/07/02
18:00

10
12/07/02
15:00

温度 [℃] / 湿度 [%]70

振動 [Gal]

温度
湿度
振動

Environment logger data (temperature, humidity, vibration)③ Influence of weather (Fig.9, 10 & 11)
environmental

990 hPa. Around this time there werechangesinatmosphericpressure990

12/07/09
10:00

980
12/07/09
04:00

985

0
12/07/08
22:00

10

日付
時刻

気圧 [hPa]

995
温度

20

12/07/08
16:00

encountered low atmospheric pressure of

1000

30

12/07/08
10:00

6th until the night of the 7th, the test

1005

12/07/08
04:00(Friday – Monday). From the night on the

1010

気圧

40

12/07/07
22:00

the course of four days, from July 6-9

1015

50

12/07/07
16:00

humidity and atmospheric pressure over

気圧

湿度

60

12/07/07
10:00

The data shows changes in temperature,

湿度70

12/07/06
22:00

conditions from changes in the weather.

12/07/06
16:00

indoor

温度 [℃] / 湿度 [%]on

温度

AD1687 FE室 除振台無 2012.07.06-07.09

12/07/06
10:00

influence

温度 Max: 29.2C Min: 24.9C
湿度 Max: 64% Min: 46.3%
気圧 Max: 1006.5hPa Min: 990.4hPa

12/07/07
04:00

The graph in Fig. 9 shows theFig.9 Environment logger data (temperature, humidity,
atmospheric pressureofaround 10-15 hPa, accompanied by 15%changes in humidity.

BM20 FE室 除振台無 2012.07.06-07.09
20.608000

repeatability results from this test are
shown in the graph in Fig. 11. During

24
22

12/07/09
04:00

23

20.598000
12/07/08
22:00

20.599000
12/07/08
16:00

was as relatively small as 200µg. The

25
スパン値

20.600000

12/07/08
10:00

measured load (20g) and the zero balance26

20.601000

12/07/08
04:00

that the variation of span between the27

20.602000

12/07/07
22:00

much as 1500µg. Further, it was noticed

28

ゼロ点

20.603000

12/07/07
16:00

to a slow drift in the zero balance of as29

20.604000

12/07/07
10:00

temperature of around 2.7°C, but this led

30

20.605000

12/07/07
04:00

in

12/07/06
22:00

changes31
温度20.606000

12/07/06
16:00

only

32

日付
時刻

12/07/06
10:00

were

温度 [C]

20.607000
スパン値/ゼロ点変化 [g]There

ゼロ点変化 [g]

温度 [C]

this period is shown in the graph in Fig.
10.

スパン値 [g]12/07/09
10:00

The change in weighing data from

Fig.10Weighing data (temperature, zero, span)

working hours on Friday repeatability
ranged between 2-8µg, however, after thisBM20 FE室 除振台有 2012.07.06-07.09

pressure and humidity due to the passingof low-pressure systems, etc. did not
influence the stability of the span value.
Rather,short-termchanges

26

6.0

25
繰り返し性

4.0

24

Fig.11

12/07/09
10:00

日付
時刻

12/07/09
04:00

22
12/07/08
22:00

23

0.0
12/07/08
16:00

2.0

Repeatability under a passing
low-pressure systemintemperature due to air conditioning, etc.
had larger effects as repeatability wasworse until 4pm on the Friday.
Repeated 24-hour data collections provided a good deal of information on the influence ofearthquakes, movement of people, air conditioning and changes in temperature, humidity or
atmospheric pressure on the repeatability of analytical balances. From the results it is clearthat the largest causes of instability in measurement data are firstly the movement of people
in the test environment, as well as effects from air conditioning; and secondly the influence ofearthquakes.
Regarding changes in humidity or atmospheric pressure, slow drift of the zero balancecaused by these factors was confirmed, but as this drift problem can be solved simply by
resetting the zero balance, any influence on repeatability can be eliminated by devising
appropriate operating procedures.
4) Environmental influence
We can say from the findings of our series of tests that the biggest disturbances on
measurement data from analytical balances are the movement and comings and goings ofpeople in room where the balances are set up as well as air movement from air conditioning
units. Further, while meteorological phenomena or earthquakes cannot be ignored,
earthquakes will end after a brief period and the only significant effect of gradual changes inmeteorological conditions on balance measurements is a drift in the zero balance. As the zerobalance can be reset each time before measurement, the influence of these environmental
factors on the repeatability of the span value can be reduced simply.
Air conditioning is essential to ensure a constant room temperature. However, it is also

温度 [C]

8.0

12/07/08
10:00

that gradual changes in atmospheric27

12/07/08
04:00

From the above results, we can see

28

10.0

12/07/07
22:00

this time.

29
温度

12.0

12/07/07
16:00

Chishima archipelago (Kuril Islands) at

30

14.0

12/07/07
10:00

Magnitude 6.1 earthquake that hit the

31

16.0

12/07/07
04:00

This was caused by a

32

18.0

12/07/06
22:00

night on Sunday.

繰り返し性(標準偏差) [ug]BM-20 1g スペック
温度 [C]
繰り返し性(標準偏差)平均 1.9 [ug] ※地震等突発の外乱を除く

12/07/06
10:00

repeatability and this occurred late at

繰り返し性(標準偏差) [ug]There was also one other disturbance in

20.0

12/07/06
16:00

period it stabilized and fell under 2µg.

clear that the slight periodic changes in temperature (temperature ripples) caused by air
conditioning also have a significant effect on the performance of analytical balances. The
influence of each of these types of disturbances cannot be completely eliminated, but it is clearthat anti-vibration table or tabletop breeze break work effectively at improving repeatability at
the microgram level.
5) Summary
Analytical balances, which are of especially high precision among weighing instruments,
are vulnerable to slight environmental changes that cannot even be felt by the user and that
invite display instability This leads to confusion over the quality of the balance itself andmakes interpreting data difficult. In this type of situation, even if the measurement device
maker conducts inspection tests to study the cause of any instability, the situation can be quite
hard to reproduce and there will be difficulties correctly determining the cause. Also, naturally,users will want to conduct measurements with the degree of precision required for their own
purposes.
In order to understand and solve this kind of problem there must be thoroughinvestigation and evaluation of the measurement environment in order to improve thisenvironment. Moreover, measurement device makers have a duty to provide information about
environmental factors to reassure users and help them effectively conduct their measurements,and offer suggestions on correct setup of the measurement location. In order to realize this it isnecessary to properly measure the environmental factors in the measurement room, and theAD-1687 environment logger, as well as the AND-MEET, or 24-hour weighing data monitoring
system, are ideal tools to evaluate these. If these tools are used correctly they can certainly
create effective conditions for precise measurement.
References
1. “Investigation of the basic performance of analytical balances”, 28th Sensing Forum (2011), The
Society of Instrument and Control Engineers (SICE)
2. “Developing the AD-1687 Weighing Environment Logger” from A&D website, Development

Story 15
3. “Solutions Provided by the BM Series Part II” from A&D website, Development Story 12