Data loggers
TS-960, TS-560, TDS-630, TDS-540, TDS-530*, TDS-602*, TDS303*, TDS-150, TDS-102*, TC-31K*, TC-32K* : No longer in production
Measurement error is not caused by initial unbalance of bridge
If the resistance of strain gauge and bridge completion resistors is notexactly the same when the strain is zero, an output voltage is yielded.
This should more or less occur in actual bridge circuits. The output
voltage is treated as an initial unbalance and deducted from theoutput voltage when strain is applied. However, it causes some error
in measured strain values. This error becomes zero by using theComplete Compensation Method of Strain.It is especially effective incases as follows, in which a large initial unbalance is expected.
••••

The leadwire is extended during the measurement.
The strain gauge is mounted on a curved surface.
Strain gauges having uneven resistance are used.
Temperature change is large during the measurement.

Non-linearity error of bridge circuit is completely corrected
The relation between the output voltage of bridge circuit and thestrain is not exactly linear. Non-linearity error becomes larger withincrease of strain. Conventional method for correcting the nonlinearity is based on condition that the initial unbalance of bridge iszero. The Complete Compensation Method of Strain works to correct
the non-linearity error even when the initial unbalance of bridge islarge. It is also effective in the following cases in addition to thecases mentioned in former clause.

Bridge output voltage e[mV]120100Output voltage
Reference

8060-100-80-60-40 -20-20-40-60

corrected
The strain gauge sensitivity is influenced by the resistance of theleadwire. In quarter bridge 3-wire method, the lead- wire resistanceis measured and the sensitivity is corrected automatically by using adata logger having the Complete Compensation Method of Strain.
When measuring multiple points of strain gauges, it is not necessary
to use lead wires of the same length for the purpose of simplifying thecorrection calculation.

Complete Correction of thermal output of strain gauge
Thermal output of strain gauge is given as data under no strain, and it
may somewhat dif fer under strained c ondition. The C omplete
Compensation Method of Strain compensates thermal output by
taking the applied strain into c onsideration. This is especiallyeffective when the thermal output is large.
(This compensation is available in TDS-630.)

Correction of error caused by replacement of strain gauge
When measuring a large strain, it is a common practice to replace thestrain gauge with a new one when the strain comes close to strain
limit of the strain gauge. In this case, accurate strain af ter thereplac ement c an be known by c or recting the measured values
referring to the strain value at the time of replacement. The Complete
Compensation Method of Strain makes this correction automatically.

Setting of true strain measurement (COMET)This is the setting for performing a measurement correcting the errorof strain value using the function called "COMET".
W h e n t h e s e n s o r m o d e i s q u a r t e r b r i d g e 3 - w i r e m et h o d, t h emeasurement value is displayedby implementing non - linearcorrection even if [Not use] isselected. By selecting Comet, it
is possible to obtain morecorrect strain value.
Half bridge common dummy canbe used only for Comet A.

COMET AThis is the correction method to correct the non-linearity error byinitial unbalance of the bridge, and this is effective when the initial
unbalance value is large. The bridge output voltage eo is measured atinitial in and memorized internally. The bridge output voltage e when
the strain is generated is c alculated when the measurement isperformed, and the correction calculation below is implemented.			
e ‒ e0		 Ԑm =		(1‒e) x (1+e 0)

COMET B (Quarter bridge 3-wire method only)

40
200Descent of sensitivity caused by the leadwire resistance isStrain Ԑ020406080

100[x103με]-80-100-120-140

Leadwire resistance is supposed to be 0 Ω.
• Strain gauge is replaced with a new one when measuring large strain.
• Initial unbalance is readjusted during the measurement.

This is used when correcting the descent of sensitivity by leadwire atthe same time as the correction method of Comet A.
The bridge output voltage eo at initial unbalance and both- ends
voltage of lead wire resistance er are measured at initial in, andmemorized internally. The bridge output voltage e when the strain isgenerated is measured at the measurement, and the calculation
below is implemented.			
e ‒ e0		 Ԑm =		(1‒e) x (1+e 0 ‒er)
When Comet B calculation is implemented, the correction calculationthat includes initial unbalance value that is recorded at initial in andboth-ends voltage of leadwire resistance is implemented from theformula above, so only the measure measurement is available. Be
sure to perform the measurement after implementing the initial in atComplete Compensation Method of Strain with Wheatstone Bridge - COMET

When measuring strain using a strain gauge, quarter bridge method iscommonly used. Quarter bridge 2-wire method is the easiest forstrain measurement, while quar ter bridge 3-wire method has anadvantage of eliminating thermal output caused by the temperaturechange of the lead wire. It is known that there may be some small
errors in measured values obtained by these methods, which arecaused by initial unbalance and non-linearity of the bridge circuit.
Most of our strainmeters already have a function of correcting nonlinearity of quarter bridge circuit. However, if we look into the matter
more closely, this function is not enough to completely correct themeasured values, for example when the initial unbalance of the bridge
is signif ic ant. Our unique technique “Complete Compensation
Method of Strain” is a method which is capable of fully correcting theerrors in measured values obtained by quarter bridge method without
being influenced by initial unbalance and non-linearity of the bridge
circuit. This method is available in our instruments listed below.

Strain Gauge

COMET: Abbreviation of Complete Compensation Method of Strain

MEASUREMENT

Complete Compensation Method of Strain with Wheatstone Bridge - COMET

the initial unbalanced status for starting measurement.

12Strain Gauge

Application example of Complete Compensation Method of Strain
Measurements using our data loggers equipped with Complete

Application example 2:Compensation Method of Strain have the advantages of the followings.

Measurement of stress concentration gauge CCFXX, CCFYX••••MEASUREMENT

Complete compensation of non-linearity
No influence of strain gauge resistanceNo influence of dummy resistanceNo need of using leadwires of the same length saving costs andspace for unnecessary leadwires• No need of correcting sensitivity change caused by leadwire
resistanceAccurate strain measurement is possible owing to the features above.
Furthermore, measurements as in the following examples become

The CCFXX and CCFYX are newly developed strain gauges having
10 grids aligned continuously without interval between each adjoining
grids. Different from the conventional stress concentration gauge
having individual grids aligned with small intervals, it can measure strain
distribution of the specimen more precisely. This strain gauge should bemeasured using our data logger with Complete Compensation Method ofStrain. The number of leadwires is reduced to 11.

possible by the use of Complete Compensation Method of Strain.

Application example 1:

CCFXX

Compensation of thermal output when using a temperatureintegrated strain gauge
Thermal output of strain gauge is automatically compensated whenmeasuring a temperature-integrated strain gauge with data logger TDS630. A polynomial representing the thermal output is attached to each

Measurement example
Strain caused by depression of bolt head (M10)strain gauge, and coefficients of the polynomial are input to TDS-630

Measuring range （mm）

before starting the measurement. Thermal output of the strain gauge-60+6

caused by the change of environmental temperature is calculated andcorrected by the TDS-630 with better accuracy than conventional method.

Real temperature and apparent strain measurement
100604020400-20

Strain20-40-600-100-20TimeDepression strain (µm/m)

Temperature
Temperature (°C)

60-80

0-50-100-150-200-250-300-350-400-450-7.5 -6 -4.5 -3 -1.5

034.5

6 7.5

Axial strain (µm/m)
0True strain after thermal output correction
10060

1000

Temperature

6040
20400Strain-2020-40

Temperature (°C)

8080

The number of leadwires is 30 which is
required for measuring a conventional
10-element strain gauge with quarter
bridge 3-wire method. The number isreduced to 11 in CCFXX/CCFYX straingauge. This is achieved by using one
leadwire for measurement of two or three-60

0-80

grids. The adjacent grid is connected
in series with one leadwire of 3-wireconnection. The resistance of this-100Time-20

adjacent grid can be ignored by using ourdata logger with Complete Compensation
Method of Strain.

131.5

Position of strain gauge (mm)Thermal output (µm/m)

Application example of Complete Compensation Method of Strain

Thermal output (µm/m)

8080