A NATIONAL MEASUREMENT GOOD PRACTICE GUIDE. No.107. Guide to the calibration and testing of torque transducers

Transcription

1 A NATIONAL MEASUREMENT GOOD PRACTICE GUIDE No.107 Guie to the calibration an testing of torque transucers

2 Goo Practice Guie 107 Measurement Goo Practice Guie No.107 Guie to the calibration an testing of torque transucers Any Robinson Inustry an Innovation Division ABSTRACT This guie escribes a collection of methos for the calibration of a torque transucer. It encompasses transucers base on ifferent technologies an transucers that operate in both static an ynamic applications. The user is expecte to select the tests suitable for their requirements.

3 Goo Practice Guie 107 Crown copyright 2008 Reprouce with the permission of the Controller of HMSO an Queen's Printer for Scotlan ISSN National Physical Laboratory Hampton Roa, Teington, Milesex, TW11 0LW Approve on behalf of the Managing Director, NPL by Susan Evans, Director, Inustry an Innovation Division

4 Goo Practice Guie 107 Contents 1 Introuction 2 General 2.1 Torque machines/rigs 2.2 Setup 2.3 Calibration 2.4 Traceability 3 Basic calibration 3.1 Non-linearity 3.2 Reproucibility 4 Aitional tests 4.1 Repeatability 4.2 Hysteresis 4.3 Creep & Creep recovery 4.4 Overloa effect 4.5 Bening effects 4.6 Output stability at zero torque 4.7 Output stability at maximum torque 4.8 Alternating torque 4.9 Torque versus angle (flexural stiffness) 4.10 Excitation voltage effects 5 Environmental tests 5.1 Temperature sensitivity at zero torque 5.2 Temperature sensitivity at maximum calibration torque 6 Dynamic tests 6.1 Frequency response (electronic) 6.2 Spee effect on zero 7 Glossary 8 Acknowlegments 9 References

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6 Goo Practice Guie Introuction This guie is aime at proviing a set of tests for the calibration, testing an evaluation of torque transucers. The guie covers a wie range of applications incluing transucers use in both static an ynamic environments. Some methos inclue in this guie will have a relevance that is limite to a particular application. The user is expecte to select the tests appropriate to the intene application. The guie allows greater flexibility an covers a wier scope than other existing stanars for static torque calibration [1, 2]. Worke examples are inclue by way of emonstration. The set of tests escribe in the guie was esigne to provie the ata that is typically foun in the manufacturer s atasheet for a torque transucer. By ocumenting a common an practical set of tests, it is hope to introuce a consistency an unerstaning that will be of benefit to both the manufacturer an the en user. During this project a number of UK torque transucer manufacturers were consulte in an attempt to collate a range of tests representative of those currently use in inustry an to ientify some common best practices. A number of transucers were teste to the methos escribe in this guie to ensure that the methos were practical an to provie ata for the worke examples. 2. General 2.1 Torque machines/rigs There are many ways of generating torque. A few alternative esigns are briefly iscusse below: Lever eaweight This consists of a set of calibrate masses that act on a calibrate lever arm. The system can be irectly applie to the transucer in the case of an unsupporte calibration beam (see figure 1). In the ieal case the lever arm will be connecte to a bearing to eliminate bening from the weights an masses an to minimise friction [3]. This type of system is use for static torque calibration an offers the best uncertainties. Figure 1. Left; An unsupporte calibration beam: right; a motor riven torque machine use for continuous torque calibration Reference torque transucer Torque can be applie using a motor or hyraulics an the torque controlle by means of a calibrate reference torque transucer in a feeback 1

7 Goo Practice Guie 107 loop (see figure 1). This type of system can be use to measure static torque but has the aitional avantage of being suitable for continuous torque calibration, whereby the applie torque is applie over a much shorter time. The isavantage of these systems is that the uncertainty of applie torque will be much higher because the system is epenant on the prior calibration of the reference. Other similar esigns may take traceability from calibrate loa cells measuring the reaction force at the en of the lever arm. Regarless of the torque facility to be use, it is important to evaluate the uncertainty of the system [4]. This shoul inclue contributions from all influencing parameters (e.g. mass, length, alignment, an environmental factors). 2.2 Setup The transucer, lea, an reaout unit shoul be consiere as a complete system for the calibration. Part numbers an serial numbers shoul be recore. The temperature at which the measurements are to take place shoul also be recore. Stabilisation - the equipment shoul be allowe to thermally stabilise for at least one hour before measurements begin. In cases where the equipment is subjecte to a significant temperature change, a longer time perio shoul be allowe for acclimatisation. The reaout unit shoul be chosen carefully so that there is aequate resolution over the whole of the torque range of interest, otherwise a lack of resolution may limit the analysis of the parameter to be measure. Resolution is given by the last active unit of the inicator, or in the case of a fluctuating reaing, half the magnitue of the largest fluctuation. The cable shoul be hanle carefully so that it has negligible influence on the transucer uner test. Particularly with small torques an goo resolutions, the hanling of the cable can have a significant effect on the output. In the ieal case a pure torque is applie to the transucer uner test. In practice the transucer will also be subject to aitional bening an parasitic forces an torques, which may affect the transucer to varying egrees [5-8]. It shoul always be the aim to keep these aitional forces to a minimum. When using unsupporte calibration beams bening forces are unavoiable. In this case it is important to be aware of the influence that bening can have on the measurement result an, where possible, to be able to quantify this. The mounting of the transucer is very important. The transucer shoul be hel as rigily as possible on the mounting plate. The fit of the squares shoul be as goo as possible to minimise any slack (see figure 2). 2

8 Goo Practice Guie 107 Figure 2. Transucer clampe in a mounting bench for an unsupporte beam calibration. The fit of the squares an rigiity of the mounting plate are important factors Bearings are often use to eliminate bening effects ue to the weight of the lever beam an weights. However epening on its quality the bearing itself may introuce errors such as friction an the performance of the bearing still requires evaluation. Alignment - practically it is very ifficult to perfectly align a transucer in a torque machine. Usually there will be some misalignment ue to the mismatch of the two axes that will give a raial, angular, or axial misalignment or any combination of the three. One way to minimise this is through the use of flexible coupling elements. The influence of bening an parasitic effects on a transucer will be epenant on the particular esign of that transucer. However the reproucibility of the evice, when calibrate in ifferent orientations, can often be a goo inicator of the influences of bening. 2.3 Calibration It is goo practice to recor all ata from the measurement process. This inclues the preloas an untare zero values. This ata can give important information, particularly in cases where the transucer oesn t behave as expecte. Following the application of the torque, a short time shoul be allowe before taking a reaing to allow the system to settle. Often this will be between 30 to 60 secons but the operator shoul allow longer if necessary. Depening on the loaing mechanism the system may be subject to inertial effects or swinging weightstacks. Some systems have amping mechanisms to limit this. A consistent wait time shoul be use across the entire measurement range to minimise time-epenant effects such as creep. 2.4 Traceability One effective metho of gaining confience in a system s performance is to compare it to another system by means of a reference torque transucer. The secon system shoul have an uncertainty similar to, if not better than, the system being evaluate. The reference transucer shoul be of the best possible quality so as to have a negligible 3

9 Goo Practice Guie 107 influence on the measurement result. In aition to the reproucibility of the transucer, something shoul be known about its long-term stability (or rift) an its sensitivity to temperature an humiity effects. 4

10 Goo Practice Guie Basic calibration Preloa the preloa is applie to be in the mechanical setup of the transucer an aapters, an to exercise the gauges. When the transucer is first put in the calibration rig it shoul be preloae 3 times to maximum torque before any measurements are mae. If the transucer is isturbe an move to a new mounting position a further preloa is require to be in the transucer. a. Preloa the transucer. b. Recor the zero torque output. c. Apply at least 5 equally space torques, increasing torque from zero torque up to an incluing the maximum torque.. At each torque, recor the output after a perio of at least 30 secons. e. If ecreasing torques are to be applie, then apply a ecreasing series back own to zero torque. f. Recor the final zero torque output. g. The transucer shoul be isconnecte an rotate in a clockwise irection. After each rotation the transucer shoul be preloae once. h. Repeat the steps so that the transucer is calibrate symmetrically (3 orientations for flange an shaft style transucers, 4 orientations for square rive transucers). 100% Applie torque 20% 0% Transucer orientation Figure 3. Loaing iagram for a square rive transucer 3.1 Departure from curve fit / Non-linearity ~ maximum ifference between the eflection an polynomial curve fit. a. For many applications, polynomial curve fits can be programme into the instrumentation. Using this metho a first orer curve fit can be use to calculate the eviation from a straight line if require. b. Calculate the mean eflection for each increasing calibration torque. c. Using the metho of least squares, compute the coefficients of a polynomial equation giving eflection as a function of applie torque.. For each calibration torque, calculate the ifference between the mean measure transucer eflection an the value compute from the equation. e. The non-linearity shall be taken as the maximum of these ifferences, when expresse as a percentage of the mean eflection. 5

11 Goo Practice Guie 107 comp Max 100 comp where: is the mean eflection; comp is eflection value calculate from the curve fit. Worke example Calibration ata comp N m Mean Value Curve fit non linearity % % % % % Cubic Curve Fit Deflection in terms of torque D = b 1 T + b 2 T 2 +b 3 T 3 b 1 = E-03 b 2 = E-08 b 3 = E-10 comp comp x100 hence eviation from curve fit/non linearity = % 3.2 Reproucibility ~ maximum change in eflection from change mounting positions. a. Calculate the maximum ifference between the eflections at each increasing calibration torque across the measurement series at ifferent orientations. b. The reproucibility shall be taken as the maximum of these ifferences, when expresse as a percentage of the mean eflection at each calibration torque. max min Max 100 where: is the mean eflection; max is the maximum eflection across the measurement series; min is the minimum eflection across the measurement series. 6

12 Goo Practice Guie 107 Worke example Calibration ata max min 100 N m Mean Value Reproucibility % % % % % hence reproucibility = 0.075% Aitional tests 4.1 Repeatability ~ maximum change in eflection from unchange mounting positions. a. Following the basic calibration proceure (see Section 3), a a secon series of increasing torques with the transucer in the zero orientation. b. Calculate the ifferences between the two series of eflections. c. The repeatability shall be taken as the maximum of these ifferences, when expresse as a percentage of the mean eflection at each calibration torque. Max where: is the mean eflection; 1 is the eflection from first series in the 0 mounting position; 2 is the eflection from secon series in the 0 mounting position. 7

13 Goo Practice Guie 107 Worke example Calibration ata N m 0 (1) 0 (2) Mean Value Repeatability % % % % % hence repeatability = 0.075% Hysteresis ~ ifference between measurements of transucer eflection for the same applie torque, one measurement being obtaine by increasing the torque from zero, the other by ecreasing the torque from the maximum calibration torque. a. Follow the basic calibration proceure in section 3, but in aition apply a single ecreasing series of torques with the transucer in the zero egree orientation. b. Calculate the ifference between the increasing an ecreasing eflections for each applie torque. c. The hysteresis shall be taken as the maximum of these ifferences, when expresse as a percentage of the increasing eflection. i ' Max i where: i is the eflection for the incremental series; i is the eflection for the ecremental series. i 100 Worke example Calibration ata N m 0 inc 0 ec Mean Value Hysteresis % % % % hence hysteresis = 0.226% i ' i i 100 8

14 Goo Practice Guie Creep ~ change in output which occurs with time while a torque transucer is subjecte to a constant torque an with all environmental conitions an other variables remaining constant [9] & Creep recovery ~ change in output which occurs with time after the torque applie to the torque transucer has been remove, with all environmental conitions an other variables remaining constant. Percentage change % 0.12% 0.08% 0.04% 0.00% Time [minutes] Percentage change % -0.04% -0.08% -0.12% -0.16% Time [minutes] Figure 4. Graphs showing creep an creep recovery curves for a typical transucer Creep a. Preloa the evice. b. With zero applie torque, wait for between 30 an 60 minutes. Recor the zero torque output. c. Apply the maximum calibration torque. Immeiately recor the initial torque output an recor the reaing thereafter at intervals not exceeing 5 minutes, over a perio not less than 30 minutes.. Subtract the initial torque output from each subsequent output. Express these ifferences as a percentage of the maximum eflection. The creep shall be taken as the maximum ifference obtaine in the first 30 minutes. e. Remove the applie torque, immeiately recor the initial zero torque output an recor the reaing thereafter at intervals not exceeing 5 minutes, over a perio not less that 30 minutes. f. Subtract the initial zero output from each subsequent output. Express these ifferences as a percentage of maximum eflection. The creep recovery shall be taken as the maximum ifference obtaine in the first 30 minutes. i Max max init 100 Creep recovery I Max 0 _ i I max 0 _ init 100 where: i is the i th eflection at maximum applie torque; init is the initial eflection at maximum applie torque; max is the maximum eflection at maximum applie torque; I 0_i is the i th inicator output at zero applie torque; 9

15 Goo Practice Guie 107 I 0_init is the initial inicator output at zero applie torque. Worke example Creep i max init 100 Creep Recovery I 0 _ i I max 0 _ init 100 Calibration ata -100 N m init Calibration ata - 0 N m 0 _ init Minutes Output Creep Minutes Creep recovery % % % % % % % % % % % % I max hence creep = 0.15% hence creep recovery = % 4.4 Overloa effect ~ effect of 110% overloa on zero output an maximum calibration torque. a. Apply the maximum calibration torque 3 times, recoring the zero torque output an the maximum calibration torque output for each torque application. Calculate the mean zero torque output an the mean eflection. b. Apply an overloa of approximately 110% of the maximum calibration torque three times, recoring the zero torque output an the overloa torque output for each application. c. Repeat step a.. Calculate the ifference between the mean zero torque output obtaine in step a an the mean zero torque obtaine in step c. Express this as a percentage of the maximum eflection. e. Calculate the ifference between the mean eflection obtaine in step a an the mean eflection obtaine in step c. Express this as a percentage of the maximum eflection. I ' 0 I '' Max ' zero output ' '' Max 100 ' - maximum calibration torque where: I ' 0 is the mean zero torque output before the overloa; 10

16 Goo Practice Guie 107 I '' 0 is the mean zero torque output after the overloa; ' is the mean eflection before the overloa; '' is the mean eflection after the overloa. Worke example zero output maximum calibration torque I Max I'' ' ' Calibration ata 0 N m 100 N m I ' N m 110 N m % % N m 100 N m ' I '' 0 ' ' ' '' Max ' hence overloa effect on zero output = % overloa effect on maximum output = % Bening effects ~ effects of sie loas on the calibration result [10]. This test is to be carrie out on a symmetrical unsupporte calibration beam. a. Calibrate to the basic calibration metho in Section 3. b. At each calibration torque recor the eflection then apply an aitional 50% of the loa on each sie of the beam, so that 150% of the applie loa is in the irection the irection the torque is to be applie an 50% of the loa is in the opposite irection. Recor the eflection. Remove the aitional loa an then apply the next increasing torque. c. Calculate the maximum ifference between the single an ouble loaing eflections at each increasing calibration torque across the measurement series an at ifferent orientations, expressing this as a percentage of the single loa eflection.. The bening parameter shall be taken as the maximum of these ifferences, when expresse as a percentage of the eflection. Max oub sin g sin g 100 where: sing is the eflection for the single loaing series; 11

17 Goo Practice Guie 107 oub is the eflection for the ouble loaing series. Worke example sing oub oub sin g sin g N m single ouble bening N m single ouble bening % % % % % % % % % % N m single ouble bening N m single ouble bening % % % % % % % % % % hence bening parameter = 0.028% between 20% & 100% of applie torque 4.6 Output stability at zero torque ~ rift in zero value. Through regular use, knowlege of a transucer s long-term stability can be built up. For a new transucer, or one with little history the following tests (4.7 & 4.8) can give some inication of the stability of the transucer. The longer the stability test the better although this has to be balance against practicalities. a. Mount the transucer in the calibration rig an allow at least 30 minutes to settle. b. With zero applie torque take a series of 15 reaings at regular time intervals over a perio of at least 48 hours simultaneously recoring temperature. c. Recor the sprea an express as a percentage of maximum eflection. I0 0 max I min 100 max where: I 0 max is the maximum output with zero applie torque; I 0 min is the minimum output with zero applie torque; max is the eflection at the maximum calibration torque. 12

18 Goo Practice Guie Output [mv/v] Time [Hours] Figure 5. Output stability at zero torque over a 56 hour perio 4.7 Output stability at maximum torque ~ rift at maximum calibration torque. a. Preloa the transucer accoring to the proceure in Section 3. b. Apply the maximum calibration torque. c. While maintaining the maximum calibration torque take a series of 15 reaings at regular time intervals over a perio of at least 48 hours simultaneously recoring temperature.. Recor the sprea an express as a percentage of maximum eflection. max min Max 100 max where: max is the maximum eflection recore over the measurement perio; min is the minimum eflection recore over the measurement perio. 13

19 Goo Practice Guie 107 Worke example Output stability at zero torque Output stability at maximum torque Calibration ata Calibration ata I 0 min min Time Output Time Output max min I0max I0min Max Max max max % % I 0 max max hence stability at zero torque = % hence stability at maximum torque = % 4.8 Alternating torque ~ zero shift when applying a clockwise torque followe by an anticlockwise torque. The toggle effect occurs when a full alternating loa cycle takes place or when the irections of preloaing an loaing iffer [11-12]. Figure 6. The graph shows the effect of alternating torque - plotte as a relative eviation from a straight line fit 14

20 Goo Practice Guie 107 a. Calibrate to the basic calibration proceure in section 3 in both clockwise an anticlockwise irections. b. Calculate the mean zero output for the clockwise calibration. Calculate the mean zero output for the anticlockwise calibration. The toggle value shall be taken as the ifference between these two values expresse as a percentage of the mean of the magnitue of the two maximum eflections for the clockwise an anticlockwise calibrations. I 0clock I 0anti 100 [ maxclock + maxanti ]/ 2 where: I 0clock is the mean zero output in the clockwise irection; I 0 anti is the mean zero output in the anti-clockwise irection; maxclock is the mean maximum eflection in the clockwise irection; max anti is the mean maximum eflection in the anti-clockwise irection. Worke example Output mv/v I 0_ clock I 0_ anti [ max I 0 clock I clock + 0 max anti anti ] / Maximum Deflection 0.13% Clockwise Anticlockwise hence alternating torque parameter = 0.13% 4.9 Torque versus angle (flexural stiffness). a. Preloa the transucer accoring to the proceure in Section 3. b. Recor the angle at zero torque. c. Apply at least 5 equally space, increasing torques from zero torque up to an incluing the maximum torque.. At each torque, recor the angle after a perio of at least 30 secons. e. If ecreasing torques are to be applie, then apply a ecreasing series of torques back own to zero torque. f. Fit a straight line to a plot of angle versus torque. Calculate the graient an express in units of /N m. g. Note: Care shoul be taken to ensure that the angle is measure is specific to the transucer an oesn t incorporate flexing in other parts of the system. 15

21 Goo Practice Guie 107 Worke example N m Angle From the graph the angle y in terms of torque x [N m] is given by y = x Excitation voltage effects ~ change in output cause by a change in the excitation voltage for a mv/v measurement system. a. Preloa the transucer accoring to the proceure in Section 3. b. Using the recommene excitation voltage apply the maximum calibration torque three times, each time taking a reaing after at least 30 secons. Calculate the mean eflection for the three reaings. c. Using the maximum excitation voltage apply the maximum calibration torque three times, each time taking a reaing after at least 30 secons. Calculate the mean eflection for the three reaings.. Calculate ifference between the two mean reaings an express as a percentage of maximum eflection. max rec 100 max where: max is the mean eflection at maximum calibration torque using the maximum excitation voltage; rec is the mean eflection at maximum calibration torque using the recommene excitation voltage. 16

22 Goo Practice Guie 107 Worke example Recommene excitation voltage Maximum exctiation voltage 8 V 12 V rec max % max rec max 100 hence ifference ue to change in excitation voltage = 0.038% 5. Environmental tests 5.1 Temperature sensitivity at zero torque ~ change in zero output with change in temperature. a. Set the temperature to 20 C an recor the zero output. b. Set the temperature to the lower limit of the compensate temperature range. Recor the zero output. c. Set the temperature to the upper limit of the compensate temperature range. Recor the zero output.. Set the temperature to 20 C an recor the zero output. e. For each temperature change calculate the change in zero torque output an ivie by the change in temperature. Take the maximum of these 3 figures an express as a percentage of maximum eflection per egree Celsius. I 0 ( temp1) I 0 ( temp2) Δ0 / eg = Δtemp Max( Δ0 / eg ) T Sens ( 0) = 100 where: I 0 (temp1) is the zero output at the first temperature; I 0 (temp2) is the zero output at the secon temperature; Δtemp is the ifference between the two temperatures; is the maximum eflection at 20 C. 17

23 Goo Practice Guie 107 Worke example Temperature sensitivity at zero torque Temp C Output mv/v % Δ0 / eg = T Sens I 0 ( temp1) I 0 ( temp 2) Δtemp Max ( Δ0 / eg ) ( 0) = 100 hence temperature sensisitvity at zero torque = % / C 5.2 Temperature sensitivity at maximum calibration torque ~ changes in the sensitivity of the transucer with change in temperature. a. Set the temperature to 20 C. b. Preloa the transucer accoring to the proceure in Section 3. c. Recor the zero torque output. Apply the maximum calibration torque three times, each time taking a reaing after at least 30 secons. Recor the zero torque output prior to the application of each torque. Calculate the mean eflection for the three reaings.. Set the temperature to the lower limit of the compensate temperature range. Follow the proceure in step c. e. Set the temperature to the upper limit of the compensate temperature range. Follow the proceure in step c. f. Set the temperature to 20 C. Follow the proceure in step c. g. For each temperature change calculate the change in the mean eflection an ivie by the change in temperature. Take the maximum of these 3 figures an express as a percentage of maximum eflection per egree Celsius. ( temp1) ( temp2) Δ / eg = Δtemp Max( Δ / eg ) T Sens ( Max) = 100 where: (temp1) is the mean eflection at the first temperature; (temp2) is the mean eflection at the secon temperature; Δtemp is the ifference between the two temperatures; is the maximum eflection at 20 C. 18

24 Goo Practice Guie 107 Worke example Temperature sensitivity at maximum calibration torque Temp C Mean eflection mv/v % Δ T Sens / eg ( temp 1) ( temp 2) = Δ temp Max ( Δ / eg ) ( Max ) = 100 hence temperature sensitivity at maximum calibration torque = 0.034% / C 6. Dynamic 6.1 Frequency response (electronic) ~ characterise by magnitue of the system s response. a. Introuce a small AC signal into the torque measuring evice an measure the output signal at the output of the inicating evice. b. Slowly increase the frequency (f) of the AC signal an measure the change in the amplitue of the output signal plotting an output against frequency graph. c. The graph shoul be reasonably linear until the frequency reaches the limits of the electronic banwith or ege of any low-pass filter. The frequency (f) at which output (f)=0.707*output Max can be taken as a measure of the banwith of the system or frequency response. Figure 7. Example of the frequency response for a system 6.2 Spee effect on zero ~ changes in the zero output of the transucer ue to rotational effects. 19

25 Goo Practice Guie 107 a. Preloa the transucer accoring to the proceure in Section 3. b. Recor the zero torque output. c. Rotate the transucer at 5 equally space rotational spees up to the maximum rotational spee of the evice. If the evice is use over a large spee range, 5 equally space rotational spees can be chosen on a logarithmic scale.. At each spee, recor the output after a perio of at least 30 secons. e. Rotate the transucer in the opposite irection an repeat the test. f. Calculate the maximum ifference between the zero outputs. g. The spee effect on zero shall be taken as this ifference expresse as a percentage of maximum eflection. I max I 0min where: I 0 max is the maximum zero output across the range of spees; I 0 min is the minimum zero output across the range of spees; is the mean eflection at the maximum calibration torque. 0 Worke example In this example a phase isplacement transucer was use. Spee effect on zero I 0 min spee rpm % phase isplacement % I o max % phase isplacement at maximum calibration torque I max I 0 min 0 hence spee effect on zero parameter = 0.51% 20

26 Goo Practice Guie Glossary Applie torque ~ the torque applie to a transucer by a torque machine or rig. Deflection ~ the ifference between the output at an applie torque an the output with no applie torque. Stabilisation ~ the process of allowing a transucer an reaout, to acclimatise to new conitions. This may be the environmental conitions in a laboratory or a change in the applie torque. Resolution ~ the smallest increment that can be measure by the inicating unit or if the reaout is fluctuating half the magnitue of the largest fluctuation. Mounting position ~ the particular orientation of a transucer in the torque machine or calibration rig. The transucer is calibrate symmetrically in several orientations to eliminate any positional epenencies. This is measure by the reproucibility of the transucer. Misalignment ~any offset between the two ens of the machine or rig to which the transucer is connecte. This offset may be raial, angular or axial. The offset will introuce parasitic forces into the transucer, which can influence the measurement result. Uncertainty ~ The applie torque for a particular rig shoul have an associate uncertainty which takes into account all of the contributing parameters an are traceable to calibration certificates for mass an length etc. Similarly the measurement result for a calibration will have an associate uncertainty. This will inclue the uncertainty of the applie torque together with transucer parameters such as reproucibility measure uring the calibration. More information on working out calibration uncertainties can be foun in some of the stanars liste in this guie. Static torque calibration ~ a process where iscrete torque increments are applie in a stepwise manner with time allowe for stabilisation of the transucer at each applie torque. Continuous torque calibration ~ a process where applie torque is applie in a continuous linear manner up to the maximum calibration torque The process takes a fraction of the time of a static torque calibration an ata from the transucer can be recore continuously. The applie torque, applie by the torque machine is usually measure by a calibrate reference torque transucer. Reference torque transucer ~a high performance transucer that can be use to measure or control the applie torque of a torque machine or as a transfer stanar to provie a comparison between ifferent torque machines. Long terms stability / rift ~ the change in the output of the transucer over a significant time perio such as the interval between successive calibrations. 21

27 Goo Practice Guie Acknowlegements The author woul like to acknowlege the support of the following iniviuals an companies, for their contributions to the project incluing technical input, provision of ata an the loan of equipment. Mr Chanchal Bahra, Instron Lt. Mr Pete Goar, Alpha Technologies UK. Mr Malcolm Habens, Datum Electronics Lt. Mr Peter Lewis, Applie Measurements Lt. Mr Paul Miles, Inustrial Measurements Lt. Mr Ben Van Millingen, Torquemeters Lt. Mr Barry Pratt, Norbar Torque Tools Lt. Mr Jeff Tanner & Dr Serghei Sanacci, Sensor Technology Lt. The pictures in figures 1 (right) an 6 are reprouce with the kin permission of the PTB. Finally the author woul like to acknowlege the financial support of the National Measurement System of the Directorate UK Department of Innovation, Universities an Skills. 9. References [1] BS 7882:1997; Calibration an classification of torque measuring evices. [2] DIN 51309:1998; Calibration of static torque measuring evices. [3] Robinson A, 2007 The Design, Development an Commissioning of a 2 kn m Torque Stanar Machine. CalLab, Jan Mar. [4] Merlo S, 2001 The uncertainty of torque primary stanars: a comprehensive analysis. Measurement 29 pp [5] Brüge A, Peschel D an Röske D, 2000 The influence of misalignment on torque transucers. Proceeings of the 16th Imeko Worl Congress, Vienna, Austria, vol. III, pp [6] Röske D, 1998 Investigation of the Influence of Disturbing Components on the Torque Measurement. Proceeings of the 16th Imeko TC3 Conference, Taejon, Korea, pp [7] Brüge A, 1996 Influence of eccentric mounting on the calibration of torque measuring evices. Proceeings of the 15th Imeko TC3 Conference, Mari, Spain, pp [8] Peschel D, 1993 Mechanical parasitic components an their influence on the calibration of torque transucers. Proceeings of the 13th Imeko TC3 Conference, Helsinki, Finlan, pp [9] Peschel D, Röske D; 1999 Determination of creep value using short-term creep. Proceeings of the 15th Imeko Worl Congress, Osaka, Japan, vol. III, pp [10] Pratt B, Robinson A, 2006 A comparison between supporte an unsupporte beams for use in static torque calibrations. Proceeings of the 18 th Imeko Worl Congress, Rio. 22

28 Goo Practice Guie 107 [11] Röske D, Peschel D, 1997 Investigations into the alternating torque calibration of torque transucers. Proceeings of the 14th Imeko Worl Congress, Tampere, Finlan, vol. III, pp [12] Röske D, 2003 Discussion on calibration results for alternating torque in comparison with single cw an acw torque calibrations. Roun table TC3 17 th Imeko Worl Congress, Dubrovnik. 23

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