Load Cell Handbook. A Technical Overview and Selection Guide PCB LOAD & TORQUE: A PCB GROUP COMPANY

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1 PCB LOAD & TORQUE: A PCB GROUP COMPANY Load Cell Hadbook A Techical Overview ad Selectio Guide PCB Load & Torque Divisio Toll-Free i the USA

2 LOAD CELL HANDBOOK Load Cell Hadbook Cotets Itroductio Overview of Load Cell Techology Strai Gage Basics Wheatstoe Bridge Axis Defiitio Output / Sesitivity Load Cell Aatomy Bedig Beam Colum Shear-Web Load Cell Classificatio Geeral Purpose Fatigue Rated Special Applicatio Applicatio Guide: Choosig the Right Load Cell...10 Rod Ed Load Cells S-Type Load Cells Caister Load Cells Low-Profile Load Cells Dual Bridge Load Cells Applicatio Selectio Chart Error Aalysis Shut Calibratio of a Strai Gage Load Cell Glossary of Terms PCB Load & Torque Divisio Toll-Free i USA

3 INTRODUCTION Rod ed load cell show o a durability test rig Itroductio This hadbook is iteded to be a guide for test egieers, lab maagers ad test techicias who use load cells for test ad measuremet applicatios for dyamometer testig, hydraulics testig, ad suspesio ad trasmissio testig, to ame a few. This guide will provide a overview of strai gage techology ad load cell aatomy icludig a descriptio of the differet types of load cells ad give istructio o how to select the right load cell for a applicatio. Typical Applicatios Materials Testig Full Vehicle Durability Testig Compoet Life Cycle Testig Torque Arm Structural Testig Weighig Press Applicatios Quality Cotrol PCB Load & Torque Divisio Toll-Free i USA

4 LOAD CELL HANDBOOK Overview of Load Cell Techology A load cell is a device that coverts a force or load ito a measureable output. Load cells ca come i multiple styles icludig hydraulic, peumatic, strai gage, piezoelectric, ad capacitace, but the scope of this hadbook will be strai gage load cells. Strai gage load cells are the most commo ad are defied as a device that coverts a force or load ito a equivalet electrical sigal or digitized load value. Strai gage load cells are desiged for precisely measurig a static weight or quasi-dyamic load or force. The force applied is traslated ito a voltage by the resistace chage i the strai gages, which are itimately boded to the trasducer structure. The amout of chage i resistace correlates to the deformatio i the trasducer structure ad hece the load applied (See Figure 1). Geeral purpose load cells iclude low profile, caister, rod-ed, S-type, fatigue rated low profile ad dual-bridge load cells. They are geerally used i automotive, aerospace, idustrial ad process cotrol applicatios. Geeral purpose load cells are suitable for a wide rage of routie static force measuremet applicatios, icludig weighig, structural testig ad material testig machies. Fatigue-rated versios are desiged for fatigue testig machies ad applicatios where high cyclic loads are preset. A high-quality fatigue-rated load cell should be compesated to miimize the effects of temperature ad barometric pressure chages as well as applied extraeous loads. It should also be resistat to fatigue failure for about 100 millio fully reversed cycles. Strai Gage Basics Whe a load is applied to a object, the object will be deformed a certai amout. The amout of deformatio the object experieces is based o the size ad material of the object as well as the size of the load applied. The ratio of the deformatio of the object to the origial size of the object is kow as strai. Strai gages are resistors that chage their resistace proportioal to load as they are deformed. They cosist of a patter of resistive foil mouted o a backig material (See Figure 2). Strai gages that are properly boded to a object will deform as the object does whe a load is applied. As the gage stretches, its resistace icreases, ad as it compresses, its resistace decreases. The amout of chage i resistace idicates the magitude of deformatio. Figure 2: Strai Gages 4 PCB Load & Torque Divisio Toll-Free i USA

5 OVERVIEW OF LOAD CELL TECHNOLOGY Wheatstoe Bridge May load cells use strai gages i a four-arm Wheatstoe bridge cofiguratio, which acts as a addig ad subtractig electrical etwork. The Wheatstoe bridge allows for compesatio of temperature effects, as well as cacellatio of sigals caused by extraeous forces. These circuits cosist of a full four-arm bridge of at least oe precisio strai gage per arm. A regulated 5 to 20 volt DC or AC rms excitatio is required to power the bridge. A simplified versio of a strai gage load cell usig the Wheatstoe bridge is depicted i Figure 3. The Wheatstoe bridge is show i Figure 4. The strai gages used i the Wheatstoe bridge all have the same resistace value creatig a balaced bridge whe o load is applied. Whe a load is applied to the load cell, the strai gages deform, which chages their resistace, creatig a bridge that is ubalaced, causig a output voltage that is proportioal to the applied load. The load applied to the load cell i Figure 3 causes the tesio gages (T1 ad T2) to stretch ad the compressio gages (C1 ad C2) to compress. A output voltage will the be set through the sigal lead wires (+S ad S) to a sigal coditioer to trasform the output voltage ito a force value (Lb, N, kg, etc.). Factors such as temperature, the legth of wire used to complete the circuit, ad gage placemet have a effect o the resistace i the bridge, creatig a error i the measured values. I precisio load cells, these effects are compesated by addig resistace to the bridge. May load cells follow a wirig code established by the Wester Regioal Strai Gage committee as revised i May The code is illustrated i Table 1. Figure 3: Model of Strai Gage Load Cell Figure 4: Wheatstoe Bridge Pi Descriptio Wire Color A + Excitatio (+P) Red B + Sigal (+S) Gree C - Sigal (-S) White D - Excitatio (-P) Black Table 1: Wester Regioal Wirig Code PCB Load & Torque Divisio Toll-Free i USA

6 LOAD CELL HANDBOOK Overview of Load Cell Techology Output & Sesitivity The output of a strai gage load cell is expressed i terms of mv/v. Therefore the output of a load cell is referred to as ratiometric, where the output is directly proportioal to the iput. For example, a load cell with a 2 mv/v output with a 10 volt excitatio applied results i a raw output of 20 mv at the defied capacity of give load cell. Most maufactures specify load cell outputs betwee 1.0 ad 5.0 mv/v, which is depedet o the gage factor ad the operatig stress (psi) of the load cell structure, although 2 mv/v is most commo. The quality of the resultat load cell sigal is depedet o several factors icludig: 1. A well regulated excitatio (typically 10 volts) 2. Quality cable with two shielded twisted pairs ad a drai 3. Istrumetatio grade amplifier I most cases a strai gage sigal coditioer is required to provide the regulatio excitatio ad coditio/amplify the sigal to a useable +/- 5 or +/- 10 volts. A wide rage of cofiguratios are available icludig models with a built-i scalable display. Sesitivity i terms of mv/egieerig uits (such as pouds or Newtos) are ot used by load cell maufacturers due to the ratiometric ature of strai gage load cells. However it s ofte useful to the ed user to express the output of a load cell i terms of sesitivity. This ca be easily calculated based o the output ad capacity of the load cell. Here are some examples: 1. A 1,000 poud capacity load cell with a 2 mv/v output ad 10 volt excitatio: (2 mv/v x 10)/1,000) or 0.02 mv/lb. 2. A 1,000 poud capacity load cell used with a sigal coditioer scaled for a 10 volts (10,000 mv) output at 1,000 pouds: (10,000 mv/1000) or 10 mv/poud The value of a strai gage sigal coditioer becomes very clear whe you cosider the differece betwee a sesitivity of 0.02 mv/poud or 10 mv/poud. Usig a sigal coditioer, you ca select the higher sesitivity. Cosequetly most load cells maufacturers offer a full rage of sigal coditioers i order to obtai the best measuremet results. Axis Defiitio Most load cells comply with the Axis ad Sese Defiitios of NAS-938 (Natioal Aerospace Stadard- Machie Axis ad Motio) omeclature ad recommedatios of the Wester Regioal Strai Gage committee. These axes are defied i terms of a "Right Haded" orthogoal coordiate system. A (+) sig idicates force i a directio which produces a (+) sigal voltage ad geerally defies a tesile force. The primary axis of rotatio or axis of radial symmetry of a load cell is the z-axis, as defied i Figure 5. Figure 5: Right Haded Orthogoal Coordiate System 6 PCB Load & Torque Divisio Toll-Free i USA

7 OVERVIEW OF LOAD CELL TECHNOLOGY Load Cell Aatomy The most critical mechaical compoet i ay strai gage based sesor is the sprig elemet. I geeral terms, the sprig elemet serves as the reactio to the applied force, load, or weight ad focuses it ito a uiform, calculated strai path for precise measuremet by the boded strai gage. Three commo structure desigs used i the idustry are bedig beam, colum, ad shear. Bedig Beam Sesor sprig elemets that employ the bedig beam structure desig are the most commo. This is because the bedig beam is typically a high-strai, low force structural member that offers two equal ad opposite surfaces for strai gage placemet. The bedig beam desig is typically used i lower capacity load cells (See Figure 6). Colum The colum type load cell is the earliest type of strai gage trasducer (See Figure 7). Although simple i its desig, the colum sprig elemet requires a umber of desig ad applicatio cosideratios. The colum should be log eough with respect to its cross sectio so that a uiform strai path will be applied to the strai gage. Whe usig this type of sesor, the ed user must beware of secod order effects as the colum load cell is susceptible to the effects of off-axis loadig. Whe usig these load cells i applicatios where sesitivity to side-loadig eeds to be miimized, it is a good idea to fid a model with a iteral spherical desig which will allow for a greater degree of off-axis loadig. Shear-Web Shear web load cells are typically catilever beams. This desig miimizes load deflectio. Uder this coditio, the surface strai alog the top of the beam would be too low to produce a adequate electrical output from the strai gage. However, if the strai gages are placed o the sides of the beam at the eutral axis where the bedig stress is zero, the state of stress o the beam side i oe of pure shear, actig i the vertical ad horizotal directio (See Figure 8). Figure 6: Bedig Beam Load Cell Figure 7: Colum Load Cell Figure 8: Shear Web Load Cell PCB Load & Torque Divisio Toll-Free i USA

8 LOAD CELL HANDBOOK Load Cell Classificatio Most load cells are classified as geeral purpose, fatigue rated, or special applicatio. Sometimes load cell suppliers will also work with you to create customized solutios for uique applicatio eeds that widely used stock products ca t meet. Geeral Purpose The geeral purpose load cell, as the ame implies, is desiged to be utilitaria i ature. These versatile load cells are commoly used for calibratio refereces, maual applicatios, ad applicatios that require slower cyclig. Withi the geeral purpose load cell market there are several distict categories: precisio, uiversal, weigh scale, to ame a few. These types of load cells are ofte selected because they are usually the least expesive. Fatigue Rated Load Cells Fatigue rated load cells are desiged for compoet durability ad fatigue test machies where highly cyclical loadig is preset. These rugged load cells are extremely resistat to extraeous bedig ad side loadig forces. They are used for material testig, compoet life cycle testig, ad structural testig. Most suppliers guaratee these load cells for 100 millio cycles. Photo courtesy of Dyamic Testig 8 PCB Load & Torque Divisio Toll-Free i USA

9 LOAD CELL CLASSIFICATION A structural compoet gaged to measure load Special Applicatios Special applicatio load cells are load cells that have bee desiged for a very specific force measuremet task. Special applicatio load cells ca be sigle- or multi-axis. There are a wide rage of special applicatio load cells especially for the automotive market, such as: Pedal Effort Crash Barrier Bumper Impact Tire Test Had Brake Skid Trailer Steerig Colum Road Simulator Horse Clamp Pedal Effort Load Cell Customized Solutios Geeral purpose load cells are quite versatile, but every so ofte, test egieers have uique applicatio eeds that are ot met by the idustry-stadard models ad specificatios. Some compaies will create custom solutios such as istrumetig customer-supplied bolts for thrust load measuremets, or trasducerizig" which meas takig a structural compoet of a system ad gagig it to measure load (for example, drive shafts usig telemetry for wireless data collectio). PCB Load & Torque Divisio Toll-Free i USA

10 LOAD CELL HANDBOOK Applicatio Guide: Choosig the Right Load Cell for the Job There are may differet types of load cells o the market which are desiged for certai uses. Here is a overview of the differet types ad their specific applicatios. Rod Ed Load Cells Need to perform load tests i small areas withi the vehicle? Rod ed load cells are a good choice for durability ad reliability testig, i-vehicle load measuremets, test rigs, ad i-lie test ad weighig applicatios especially for testig i small spaces, like i-lie with vehicle tie rods, ad istaces where sesitivity to side loadig eeds to be miimized. S-Type Load Cells S-type load cells are side-mouted strai gage-based sesors used for weighig ad geeral force measuremet applicatios. It is a good idea to select oe with a log strairelieved itegral cable with pigtail leads that are stripped ad tied for electrical iterface. These load cells are most commoly used for light structural performace testig o automotive systems such as doors, hoods ad truks, ad automotive lifecycle testig o compoets such as higes, latches ad hadles, bushigs ad sprigs, ad seatbacks. These are a good choice whe you eed a low-cost, high performace load cell. Figure 11: Rod Ed Load Cells Figure 12: S-Type Load Cells Caister Load Cells Caister load cells are typically used for weighig, quality cotrol, dyamometers, tactile forces, ad static material test machies. Caister style load cells have low mass (less tha oe lb.) ad low capacity (25 to 300 lbs). They also iclude a built-i moutig base ad the same thread o both sides, makig them easy to istall. This type of load cell is used for applicatios such as opeig ad closig car doors, auto compoet tests, truk doors, ad switch test stads. Figure 13: Caister Load Cells 10 PCB Load & Torque Divisio Toll-Free i USA

11 APPLICATION GUIDE: CHOOSING THE RIGHT LOAD CELL FOR THE JOB Fatigue rated load cells measure impact forces durig automotive crash studies Low-Profile Load Cells Low profile load cells, sometimes referred to as pacake load cells, iclude fatigue-rated ad geeral purpose types. They are geerally offered i a wide capacity rage across a few differet mechaical packagig/sizes. Low-profile load cells feature a advaced structural desig that makes them extremely durable ad accurate. Their greatest attribute is that they are idustry-stadard, so you ca geerally use oe maufacturer's load cell iterchageably with aother's. These load cells are also kow for their overall capability to hadle extraeous loads due to misaligmet without mechaical failures. Low profile load cells are very forgivig to geeral mistakes made durig istallatio (such as misaligmets bedig loads or momets ad shear loads). This type of load cell also usually comes with two istallatio optios with a base ad without a base. To perform i a liear ad predictable maer, the outside diameter of the load cell must be bolted to a flat rigid surface. To esure that they ca also be properly mouted i applicatios where there is o flat rigid surface, they iclude a factory istalled base that provides a coveiet threaded attachmet poit for easy istallatio ad use i tesio ad compressio. For best performace, repeatability ad accuracy, it s a good idea to select oe with the base icluded ad permaetly istalled. These types of load cells are used for a wide rage of geeral force measuremet applicatios, icludig weighig, dyamometer use, ad static material test machies. Dual Bridge Load Cells Dual bridge load cells are fatigue rated load cells that iclude a dual output feature that offers sesor redudacy ad the ability to provide cotrol feedback from oe sesor while the other is used for data acquisitio. Additioal features iclude low deflectio, high accuracy ad repeatability, thermal compesatio ad momet compesatio. Dual bridge load cells are most ofte used i aerospace ad defese testig, where oe output cotrols the test stad/process, ad the other output for data recordig. PCB Load & Torque Divisio Toll-Free i USA

12 LOAD CELL HANDBOOK Applicatio Selectio Whe decidig which type of load cell you eed, cosider the followig applicatio questios to help you select the right oe. Whe decidig which type of load cell you eed, cosider the followig applicatio questios to help you select the right oe. Determie the capacity required: What is the maximum expected load? What is the miimum expected load? What is the typical expected load? What are the dyamics of the system (frequecy respose, voltage requiremets, coector type, etc.)? What are the maximum extraeous loads that the load cell will be subjected to? How will the load cell be itegrated ito the system: What are the physical costraits (height, diameter, moutig threads, etc.)? Will the load cell be i the primary load path or will the load cell see forces idirectly? What type of eviromet will the load cell be operatig i: What will the maximum temperature be? What will the miimum temperature be?? Will there be ay cotamiats preset (water, oil, dirt, dust, etc.)? What accuracy is required: What is the o-liearity specificatio required? What is the hysteresis specificatio required? What is the repeatability specificatio required? What, if ay, cross-talk specificatio is required (for multi-axis load cells)? What will the humidity be? Will there be ay cotamiats preset (water, oil, dirt, dust, etc.)? See glossary for defiitio of the terms above. 12 PCB Load & Torque Divisio Toll-Free i USA

13 APPLICATION SELECTION CHART Photo Courtesy of NASA Lagley Research Ceter Dual bridge load cells i use o a life cycle test of a aircraft wig box Error Aalysis Accuracy iformatio for load cells is commoly reported i terms of idividual errors. These errors iclude but are ot limited to: No-Liearity Hysteresis No-Repeatability See glossary for defiitio of the terms above. Effect of Temperature o Zero Ubalace Effect of Temperature o Output Load cells are typically desiged ad maufactured to miimize these errors to idustry stadard levels. Below is a summary of the performace stadards by idustry. Typical Load Cell Performace Requiremets by Market Parameter Idustrial Automotive Test & Measuremet Aerospace & Defese No-Liearity 0.25 % to 1% 0.1 to 1% 0.05% to 0.25% 0.04% to 0.06% Hysteresis 0.25% to 1% 0.1 to 1% 0.05% to 0.25% 0.04% to 0.06% Repeatability 0.1% to 0.5% 0.05% to 0.1% 0.05% to 0.02% 0.02% to 0.01% The customer ca combie these idividual errors to establish the maximum possible error for the measuremet or just examie the applicable idividual error. If the temperature is stable durig the test, the temperature related errors ca be igored. If the sesor is used for icreasig load measuremet oly, the the hysteresis error ca be igored. If the load measuremet is ear the full capacity, the liearity error ca be igored. If the capability exists to correct the data through liearizatio-fit or a look-up-table, the error i the measuremet ca be miimized. Ofte overlooked is the error due to the presece of o-measured forces ad bedig momets. Eve though the sigle axis of measuremet sesors are desiged ad built to withstad these extraeous loads, the errors due to them are preset. The measuremet egieer ca desig the set-up to elimiate or miimize these extraeous loads, however, if these loads are preset, the errors due to them should be cosidered. A typical idustry-accepted meas of combiig idividual errors is Root Sum Square, which assumes that the idividual errors do ot simultaeously occur. Note: Figures 9 ad 10 show exaggerated plot data to better graphically explai the load cell errors. I practice, load cell errors will appear much closer to the projected lie from zero to rated output to coform to idustry ad specified stadards. For defiitios of these errors, see the Glossary of Terms sectio at the ed of this documet. Figure 14: No-Liearity & Hysteresis Figure 15: Repeatability PCB Load & Torque Divisio Toll-Free i USA

14 LOAD CELL HANDBOOK Shut Calibratio of a Strai Gage Load Cell Shut calibratio is the kow electrical ubalacig of a strai gage bridge by meas of a fixed resistor that is placed, or shuted, across oe leg of the bridge. The Wheatstoe Bridge used i strai gage load cells are typically field-calibrated usig the shut calibratio techique (See Figure 15). Purpose Shut calibratio is a method of periodically checkig the gai or spa of a sigal coditioer, which is used i cojuctio with a strai gage based trasducer, without exposig the trasducer to kow, traceable, physical iput values. If required, adjustmets ca the be made to the sigal coditioer to isure accurate measuremet results. A strai gage bridge is i balace whe the host mechaical structure is uloaded ad ustressed. As the host structure (diaphragm, bedig beam, shear beam, colum, etc.) is loaded or stressed, the Wheatstoe Bridge becomes ubalaced, resultig i a output sigal that is proportioal to the applied load. Shut calibratio stimulates the mechaical iput to a trasducer by ubalacig the bridge with a fixed resistor placed across, or i parallel with, oe leg of the bridge. For tesio shut calibratio, the shut resistor (R ST ) is shuted across the +excitatio (+P) ad +sigal (+S) leg of the bridge. For a compressio shut calibratio, the shut resistor (R SC ) is shuted across the excitatio (-P) ad +sigal (+S) leg of the bridge. Figure 16: A Wheatstoe Bridge circuit showig the locatio for coectig the appropriate shut resistor for the purpose of simulatig either a tesio or compressio iput. Method Here are step-by-step istructios for shut calibratio of a strai gage load cell. 1. Coect the trasducer to a appropriate strai gage sigal coditioer ad allow adequate time for the system to stabilize. 2. Apply a full-scale N.I.S.T. traceable, mechaical iput (or load) to the trasducer. 3. Adjust the sigal coditioer s gai or spa cotrols, as required, to obtai a full-scale electrical output sigal, ad/or umeric display that represets the applied, mechaical iput quatity. 4. Remove the mechaical iput (or load). 5. Place a shut calibratio resistor across a appropriate leg of the Wheatstoe Bridge (as discussed above). 6. Record the value of the sigal coditioer s output sigal ad/or umeric display. This value is the shut calibratio value, or equivalet load. 7. It is importat to ote that the shut calibratio value is specific for the particular shut resistor used.this value, ad the particular resistor, are ow matched to the trasducer ad form the basis of the trasferable shut calibratio. Summary Shut calibratio is accepted throughout the idustry as meas of periodic calibratio of a sigal coditioer ad trasducer betwee calibratios of kow, applied, traceable, mechaical, iput values. Cosequetly, most all strai gage trasducer maufacturers collect ad supply shut calibratio data, alog with a shut calibratio resistor, as a stadard feature. 14 PCB Load & Torque Divisio Toll-Free i USA

15 SHUNT CALIBRATION OF A STRAIN GAGE LOAD CELL Glossary of Terms Accuracy: Stated as a limit tolerace, which defies the average deviatio betwee the actual output versus theoretical output. I practical trasducer applicatios, the potetial errors of o-liearity, hysteresis, o-repeatability ad temperature effects do ot ormally occur simultaeously, or are they ecessarily additive. Therefore, accuracy is calculated based upo RMS value of potetial errors, assumig a temperature variatio of ±10 F (±5.5 C), full rated load applied, ad proper set-up ad calibratio. Potetial errors of the readout, cross-talk, or creep effects are ot icluded. Ambiet Coditios: The coditios (humidity, pressure, temperature, etc.) of the medium surroudig the trasducer. Ambiet Temperature: The temperature of the medium surroudig of trasducers. Calibratio: The compariso of trasducer output agaist stadard test loads. Calibratio Curve: A record (graph) of the compariso of trasducer output agaist stadard test loads. Combied Error: (o-liearity ad hysteresis) the maximum deviatio from a straight lie draw betwee the origial o-load ad rated load outputs expressed as a percetage of the rated output ad measured o both icreasig ad decreasig loads. Compesatio: The utilizatio of supplemetary devices, materials, or processes to miimize kow sources of error. Creep: The chage of trasducer output occurrig with time, while uder load, ad with all evirometal coditios ad other variables remaiig costat. Note: Usually measured with rated load applied ad expressed as a percet of rated output over a specific period of time. Creep Recovery: The chage i o-load output occurrig with time, after removal of a load, which has bee applied for a specific period of time. Cross-Talk: With oe compoet loaded to capacity, ad the other uloaded, the output of the uloaded compoet will ot exceed the percetage specified of its full-scale capacity. Deflectio: The chage i legth alog the primary axis of the load cell betwee o-load ad rated load coditios. Drift: A radom chage i output uder costat load coditios. Error: The algebraic differece betwee the idicated ad true value of the load beig measured. Excitatio, Electrical: The voltage or curret applied to the iput termials of the trasducer. Fatigue Capacity: Capacity as percetage of the omial load limit capacity, ad based o 100 X 106 cycles (miimum) from zero to full fatigue capacity ad 50 X 106 cycles (miimum) from full fatigue capacity tesio to full fatigue capacity compressio load. Full Scale: The desiged upper operatig limit of a give trasducer i egieerig uits (pouds, grams, kilograms, or Newtos) Hysteresis: The maximum differece betwee the trasducer output readigs for the same applied load, oe readig obtaied by icreasig the load from zero ad the other by decreasig the load from rated load. Note: Usually measured at half rated output ad expressed i percet of rated output. Measuremets should be take as rapidly as possible to miimize creep. Isulatio Resistace: The DC resistace measured betwee the trasducer circuit ad the trasducer structure. Note: Normally measured at 50 Volts DC ad uder stadard test coditios. Natural Frequecy: The frequecy of free oscillatios uder o load coditios. Kip: A o-si uit of force. It equals 1000 pouds-force. Nomial Load Limit Capacity: It is the desiged ormal maximum capacity of a trasducer. Output sesitivity of the trasducer is based o this capacity uless specified. No-liearity: The maximum deviatio of the calibratio curve from a straight lie draw betwee the o load ad rated load output, expressed as a percetage of the rated output ad measured o icreasig load oly. Output: This sigal (voltage, curret, etc.) produced by the trasducer. Note: Where the output is directly proportioal to excitatio, the sigal must be expressed i terms of volts per volt, volts per ampere, etc., of excitatio. Output, Rated: The algebraic differece betwee the outputs at o-load ad at rated load. Overload Ratig: The maximum load i percet of rated capacity, which ca be applied without producig a permaet shift i performace characteristics beyod those specified. Primary Axis: The axis alog which the trasducer is desiged to be loaded; ormally its geometric ceterlie. Rated Capacity (Rated Load): The maximum axial load that the trasducer is desiged to measure withi its specificatios. Repeatability: The maximum differece betwee trasducer output readigs for repeated loadig uder idetical loadig ad evirometal coditios. Resolutio: The smallest chage i mechaical iput, which produces a detectable chage i the output sigal. Sesitivity: The ratio of the chage i output to the chage i mechaical iput. Shut Calibratio: Electrical simulatio of trasducer output by isertio of kow shut resistors betwee appropriate poits withi the circuitry. Shut-to-load Correlatio: The differece i output readigs obtaied through electrically simulated ad actual applied loads. Stadard Test Coditios: The evirometal coditios uder which measuremets should be made, whe measuremets uder ay other coditios may result i disagreemet betwee various observers at differet times ad places. These coditios are a follows: Temp: 72 F ±3.6 F (23 C ± 2 C) Relative Humidity: 90% or less Barometric Pressure: ich Hg Static Extraeous Load Limits: Static Extraeous Load Limits are calculated such that oly oe extraeous load (FX or FY or MX or MY or MZ) ca be applied simultaeously with 50% of the omial load limit applied. Temperature Effect o Output: The chage i output due to a chage i trasducer temperature. Note: Usually expressed as a percetage of load readig per degree Fahreheit chage i temperature. Temperature Effect o Zero Balace: The chage i zero balace due to a chage i trasducer temperature. Note: Usually expressed as the chage i zero balace i percet of rated output per degrees Fahreheit (chage i temperature). Temperature Rage, Compesated: The rage of temperature over which the trasducer is compesated to maitai rated output ad zero balace withi specified limits. Temperature Rage, Usable: The extremes of temperature withi which the trasducer will operate without permaet adverse chage to ay of its performace characteristics. Termial Resistace: The resistace of the trasducer circuit measured at specific adjacet bridge termials at stadard temperature, with o-load applied, ad with the excitatio ad output termials ope-circuited. Termial Resistace, Excitatio: The resistace of the trasducer circuit measured at the excitatio termials, at stadard temperature, with o-load applied, ad with the output termials ope-circuited. Termial Resistace, Sigal: The resistace of the trasducer circuit measured at the output sigal termials, at stadard temperature, with o-load applied, ad with the excitatio termials ope-circuited. Traceability: The step-by-step trasducer process by which the trasducer calibratio ca be related to primary stadards. Zero Balace: The output sigal of the trasducer with rated excitatio ad with o-load applied, usually expressed i percet of rated output. Zero Retur: The differece i zero balace measured immediately before rated load applicatio of specified duratio ad measured after removal of the load, ad whe the output has stabilized. Zero Shift, Permaet: A permaet chage i the oload output. Zero Stability: The degree to which the trasducer maitais its zero balace with all evirometal coditios ad other variables remaiig costat. PCB Load & Torque Divisio Toll-Free i USA

16 LOAD CELL HANDBOOK Photo courtesy of Dyamic Testig PCB Load & Torque Divisio, is a maufacturer of high quality, precisio load cells, torque trasducers, ad telemetry systems, located i Farmigto Hills, Michiga, USA. I additio to the quality products produced, the divisio offers may services icludig: A2LA Accredited Calibratio for torque, force, ad related istrumetatio; a A2LA Accredited Threaded Fasteer Testig Laboratory; ad complete ad reliable custom stai gagig. PCB Load & Torque products ad services fulfill the test ad measuremet eeds of umerous idustries icludig: Aerospace & Defese, Automotive, Medical Rehabilitatio, Material Testig, Textile, Process Cotrol, Robotics & Automatio, ad more. PCB s RS Techologies product lie icludes test systems ad threaded fasteer torque/agle/tesio systems ideal for use i the Automotive, Aerospace & Defese, Power Geeratio idustries, ad for product assembly by maufacturers or processors of threaded fasteers or other compaies that use threaded fasteers to assemble their products. The expert team of Desig, Egieerig, Sales, ad Customer Service idividuals draw upo vast i-house maufacturig resources to cotiually provide ew, more beeficial sesig solutios. From ready-to-ship stock products, to custom-made specials, PCB proudly stads behid all products with services customers value most, icludig 24-hour techical support, a global distributio etwork, ad the idustry's oly commitmet to Total Customer Satisfactio. For more iformatio please visit The Global Leader i Sesors ad Istrumetatio For All Your Applicatios Toll-Free i USA aerosales@pcb.com Toll-Free i USA automotivesales@pcb.com Toll-Free i USA imi@pcb.com Toll-Free i USA sales@larsodavis.com LOAD & TORQUE A PCB PIEZOTRONICS DIV Idoplex Circle, Farmigto Hills, MI USA Toll-Free i the USA hour SesorLie SM Fax ltifo@pcb.com website ISO 9001 CERTIFIED A2LA ACCREDITED to ISO Toll-Free i USA ifo@modalshop.com 2014 PCB Group, Ic. I the iterest of costat product improvemet, specificatios are subject to chage without otice. PCB, ICP, Modally Tued, Spidler, Swiveler ad TORKDISC are registered trademarks of PCB Group. SoudTrack LXT, Spark ad Blaze are registered trademarks of PCB Piezotroics. SesorLie is a service mark of PCB Group. All other trademarks are property of their respective owers. LT-LoadCellHadbook-1214 Prited i U.S.A. Toll-Free i USA ifo@pcb.com Visit for a complete list of global sales offices