A load cell answers the question "how much force is this?" with a voltage. Gauges fixed to a deliberately shaped piece of metal detect how far it gives under load, a bridge circuit turns that into a signal, and a calibration performed against known weights converts the signal into pounds.
People tend to read a datasheet as though a load cell has one accuracy. It rarely does. There are several distinct ways a sensor can be wrong, they're specified separately, and on any product offered in a range of configurations, some of those numbers can change depending on how you order it.
That last point deserves more attention than it usually gets. A series offering multiple sizes, bores, materials or mounting arrangements is not one product with a single specification — it is a family, and the datasheet describes the family. Footnotes matter. A line reading "except on the following options" is not fine print; it is the manufacturer telling you where a genuine engineering trade sits, and it is usually the most useful sentence on the page.
On through-hole designs, the trade is geometric and unavoidable. The sensing structure is the ring of metal between the bore and the outside diameter. Enlarge the hole without enlarging the body and that ring gets thinner, leaving less material both to carry the load and to strain predictably under it. Manufacturers manage this by offering families of increasing outside diameter — but within any single body size, the largest available bores are working with the least material, and at some point that shows up in the specifications rather than being absorbed silently.
Which is exactly what you want. A specification that changes at the extremes of a range is a manufacturer being honest about physics rather than quoting one flattering number and hoping. It also gives you something actionable: if your application needs the biggest hole, you know what it costs; if accuracy matters more than clearance, you know to size differently.
Sensors of this kind — heat-treated 17-4 PH stainless, sealed gauges, generous bores — end up around structural fasteners, tie rods, hydraulic cylinder rods, ball screws, shafts through bearings, and press and clamping systems, wherever a large component already exists and the force running through it needs measuring rather than estimating.
Conventional in principle. Worth understanding in detail, because that detail is what tells you which configuration to order.
Producing a reading. Nothing is measured until the bridge has power behind it; 10 VDC is what these expect. Put weight on the ring and each gauge reports its share by shifting resistance, at which point the bridge stops sitting balanced and hands you a few millivolts. How many millivolts depends partly on how many volts you started with, which is the reason the sensitivity figure is written as one over the other. The electronics condition it and the certificate on file converts it. Change the supply from what that certificate assumed and you have shifted every subsequent number by the same proportion.
Why a thin ring behaves differently. Nonlinearity describes how far a sensor's output strays from a straight line between zero and capacity, and it exists because metal under stress doesn't respond in a perfectly proportional way. How much it strays depends on the geometry doing the work. A generous cross-section stressed modestly stays close to linear. A narrow annulus working harder for the same load has more room to depart from the line. This is the mechanism behind a nonlinearity specification that loosens at the largest bore sizes — not a manufacturing compromise, but the predictable consequence of asking less material to do the same job.
Which specification actually governs your result. Nonlinearity matters most when you calibrate at one point and measure at another, because that's when the departure from the straight line becomes your error. If you work at or near a single force and your system is calibrated there, a looser nonlinearity figure costs you far less than the number suggests. Conversely, if you sweep across the full range and need every point to be right, nonlinearity is the specification that decides your data quality. The same figure means different things to different users.
Load still has to enter evenly. On a three-inch body the bearing face is wide, and hardware sized for the component passing through can easily contact only part of it. What presses on each face should be flat, hard, and matched to the sensor's annular dimensions rather than to the bolt or rod.
And the bore is still clearance. Nothing running through the middle should touch the wall, because contact adds friction and lateral force indistinguishable from real load. Larger holes give more room to achieve this, though a rod that clears when cold and unloaded may not once the assembly is at working temperature and deflecting.
When a series offers dozens of configurations, selection is a matter of working out which constraints are fixed and which are yours to choose. Our application engineers do this daily and can usually place you quickly — but the reasoning is worth understanding.
Identify what is already decided for you. Usually the bore, because a component exists that has to pass through it, and often the outside diameter, because a finite space exists to fit into. Those two are frequently not negotiable, and everything else gets chosen around them. Establishing them first saves working through options that were never available.
Read the footnotes before comparing options. Where a datasheet notes that a specification differs for particular configurations, that note is telling you where the engineering trade sits. It is worth finding before you choose rather than after, because it may change which option you want — and because a specification quoted without its exceptions is not the specification you will actually receive.
Then ask what your accuracy requirement really is. This is where people over-specify. A tighter figure is genuinely worth paying for when readings feed a pass/fail decision, support a quality record, or have to be defended to an auditor. It matters much less when you are monitoring for gross change, watching a trend, or confirming that a joint has not lost its clamp. Be honest about which you are doing, because the answer may make a looser specification perfectly acceptable and open up a configuration that fits better mechanically.
Size capacity for what could happen, not what should. On assemblies involving fasteners and hydraulics, the force available during installation or from a stuck valve frequently exceeds anything the design intends. Check your credible worst case against the safe overload figure, and add a mechanical limit where the potential exists to exceed it.
Provide bearing surfaces worthy of the sensor. Hardened, flat, and covering the annular face on both sides. On larger bodies this often means specifying washers rather than accepting what the assembly already has.
Confirm direction, environment and readout. Certification here covers downward force, making any pull in your application a pre-order discussion. On environment, sealed gauges handle dust, debris and everyday moisture, though hermetic sealing they are not — describe wet or chemically aggressive service to us instead of assuming coverage. As for what the sensor talks to, options run from a bare regulated supply through an amplifier signal conditioner module to a digital display capable of alarms, analog output and logging. Multiple units in service is the situation Cal-Teds plug and play was made for, since each cell then carries its own calibration wherever it goes.
Four things point us to the right configuration: the component going through the middle, the room surrounding it, the forces at play, and — the one people leave out, though it often decides the answer — what the reading is ultimately for. We hold standard products in stock for prompt dispatch, and schools and universities are eligible for reduced pricing.
THD Series Load Cell Applications.
The Transducer Techniques THD Series through-hole donut load cells, featuring a versatile design with multiple through-hole diameter options and constructed from heat-treated 17-4 PH stainless steel, have diverse applications across various industries where precise force measurement is crucial.
- Industrial Automation: THD Series load cells are integrated into industrial automation systems for monitoring and controlling forces in robotic applications, material handling processes, and manufacturing operations. They ensure precise assembly and quality control in industries such as automotive, electronics, and consumer goods manufacturing.
- Robotics and Automation: These load cells are used in robotics and automation systems for force sensing applications, including robot end-effector force control, pick-and-place operations, and quality checks on assembly lines.
- Force and Torque Measurement: THD Series load cells are essential for precise force and torque measurement in research, testing, and quality control across various industries. They provide accurate data on forces and torques applied in both tension and compression modes.
- Materials Testing: In materials testing laboratories, THD Series load cells are employed for various testing applications, including tensile and compressive testing of materials such as metals, plastics, ceramics, and composites. They help assess material properties and product quality.
- Automotive Testing: Automotive manufacturers and testing facilities use THD Series load cells for quality control and testing of vehicle components, such as suspension systems, steering mechanisms, and brake systems. These load cells contribute to evaluating the performance and safety of automotive parts.
- Aerospace and Aircraft Testing: The aerospace industry relies on THD Series load cells for structural testing of aircraft components, flight control systems, and materials used in aircraft construction. They play a crucial role in ensuring the reliability and safety of aerospace equipment.
- Product Development: Engineers and researchers use THD Series load cells during product development and prototyping. They assist in evaluating the performance, durability, and structural integrity of new designs and components.
- Biomechanics and Medical Devices: In biomechanics research and medical device testing, THD Series load cells measure forces applied to the human body or medical devices during experiments and analysis. This data is vital for understanding physiological processes and validating medical equipment.
- Educational Laboratories: Educational institutions incorporate THD Series load cells into engineering and physics laboratories to teach students about force measurement principles and conduct experiments related to mechanics and materials science.
- Custom Machinery and Equipment: Manufacturers and research facilities integrate THD Series load cells into custom-built machinery and equipment designed for specialized testing and manufacturing processes that require precise force measurement.
The Transducer Techniques THD Series through-hole donut load cells, with their versatile design and multiple through-hole diameter options, are valuable tools across a wide range of industries and applications where accurate and reliable force measurement is crucial for safety, quality, and performance assessment.
Frequently Asked Questions
What are the nine THD bore options?
The model suffix identifies the through hole: -P 0.128" (1/8), -Q 0.193" (3/16), -R 0.266" (1/4), -S 0.391" (3/8), -T 0.532" (1/2), -V 0.656" (5/8), -W 0.781" (3/4), -Y 1.032" (1"), and -Z 1.281" (1-1/4"). Nine options is the widest bore selection we offer, taking the through-hole format from small fasteners right up to substantial rods and shafts.
Why do the -Y and -Z bores have a different nonlinearity specification?
Because at those bore sizes there is measurably less material doing the work. Nonlinearity is specified at 0.25% of rated output across the series, except on the -Y (1") and -Z (1-1/4") hole diameters, where it is 0.5% of rated output. The sensing structure on a donut is the ring between the bore and the outside diameter, and opening the hole to an inch or more within a 3.00 inch body leaves a comparatively narrow annulus working harder for the same load. A narrower ring under higher stress departs further from a perfectly straight response. We publish the difference rather than quoting a single figure because it's a real effect and you should be able to plan around it.
Does the 0.5% nonlinearity on -Y and -Z mean those models are less accurate overall?
Only in one specific respect. Hysteresis stays at 0.25% of rated output, nonrepeatability at 0.1%, and zero balance at 1.0% across every bore in the series — the -Y and -Z differ on nonlinearity alone. That matters because nonlinearity describes deviation across the range: it costs you most when you calibrate at one force and measure at another, and comparatively little when you work at or near a single load with the system calibrated there. If your application sits at one point on the curve, the larger bores may cost you far less than the number suggests.
What capacities does the THD Series cover?
Nine: 2,000, 3,000, 5,000, 7,500, 10,000, 15,000, 20,000, 30,000, and 50,000 lb. With nine bores across nine capacities, that's eighty-one configurations from a single series — and every one is the same price. Bore and capacity are independent choices here, with the single caveat that the two largest bores carry the different nonlinearity figure noted above.
Why is the THD's outside diameter 3.00 inches?
Because a 1-1/4 inch hole and a 50,000 lb rating have to coexist in the same body. Bore, outside diameter and capacity all draw on the same cross-section of material, so a three-inch body is what leaves enough annulus for the largest bore in the range to still carry serious load. It's also why the specification note applies to the top two bores rather than to the whole series — the geometry runs out of margin at the extreme end, not across the board.
What can pass through a 1-1/4 inch bore?
At that size you're well past fasteners and into structural components: large tie rods, hydraulic cylinder rods, ball screws, drive shafts, and press columns. The measurement question changes accordingly. Rather than verifying how tight someone made a joint, you're measuring the force a machine is actually generating or reacting — which is usually a more valuable number and one that's difficult to obtain any other way without dismantling something.
Are the THD's strain gauges sealed?
Yes, bonded foil gauges sealed for protection in industrial environments, which suits a sensor destined to sit inside machinery for a long time. To be precise about the limit: that's protection against dust, debris and moderate moisture rather than hermetic sealing, so directed wash-down or corrosive exposure is a different requirement. Tell us what the environment is genuinely like and we'll give you a straight answer on whether the THD is suitable.
What is the THD's deflection, and how does temperature affect it?
Deflection is 0.002 inches at rated output, consistent across the series. Compensation runs 60° to 160°F, with a safe range of −65° to 200°F; inside the compensated band, output drifts 0.005% of load per °F and zero drifts 0.01% of rated output per °F. That deflection figure is worth noting on a captured sensor — two thousandths of an inch means adding a THD to a loaded assembly doesn't meaningfully change how that assembly behaves.
What is the THD made from?
Heat-treated 17-4 PH stainless steel with bonded foil strain gauges. The alloy is doing genuine work here: 17-4 PH is a precipitation-hardening stainless whose heat treatment forms fine strengthening particles throughout the metal without distorting a precision part. That strength is what permits a 1-1/4 inch hole through a three-inch body while still supporting 50,000 lb, and the stainless base contributes corrosion resistance for long installed service.
Can I get the THD with the plug-and-play TEDS option?
Yes, OPT-TEDS is available and stores the unit's calibration data at the connector so a compatible instrument reads and applies it automatically. On a series with eighty-one configurations — some of which carry a different nonlinearity figure — that's more than convenience. It means the calibration travelling with each sensor is unambiguously the right one, rather than depending on records matching labels correctly.
Questions From The Field
Should I avoid the -Y and -Z bores because of the nonlinearity figure?
Not automatically — it depends entirely on how you use the reading. If your system is calibrated at or near the force you actually work at, nonlinearity contributes little, because you're measuring close to the point where the curve was pinned down. If you sweep across a wide range and need every point accurate, it becomes your dominant error and a smaller bore is worth arranging for. The other consideration is that these are the only bores that will accept a one-inch or larger rod, so if that's what has to pass through, the choice may already be made. Tell us your force range and calibration point and we can tell you what the difference actually costs you.
Is there a way to get a large bore without the nonlinearity penalty?
Within the THD, the specification follows the bore, so -Y and -Z carry the 0.5% figure regardless of capacity. What sometimes helps is reconsidering the installation rather than the sensor: if the component passing through could be reduced in diameter at the sensor location — a stepped shaft, a shoulder, or a shorter sleeve section — a smaller bore becomes available and the tighter specification with it. That isn't always practical, but it's worth a moment's thought before accepting the trade. Send us the geometry and we'll look at it with you.
How do I choose between the THC and THD?
Bore requirement and capacity usually settle it. The THC has a 2.00 inch body with bores to 5/8 inch and capacities to 10,000 lb; the THD's 3.00 inch body takes bores to 1-1/4 inch and capacities to 50,000 lb. If your component fits a THC bore and your force is within its range, the smaller body is easier to fit into an assembly. Once you need a 3/4 inch or larger hole, or more than 10,000 lb, the THD is where the range continues. Note also that the specification note on -Y and -Z has no equivalent on the THC, since that series doesn't reach those bore sizes.
My rod is 1 inch. Should I order -Y or step up to -Z?
A one-inch rod through a 1.032 inch bore leaves very little clearance — around sixteen thousandths of an inch all round — which is tight once you account for thermal growth, deflection under load, and any tolerance on the rod itself. If the installation can accommodate it, -Z gives you substantially more room without changing the nonlinearity figure, since both bores carry the same 0.5% specification. There's no penalty for the extra clearance and a real risk in having too little.
What bearing surfaces does a three-inch cell need?
Hardened, flat, and sized against the sensor rather than against whatever passes through it. This is the most common installation error on the larger through-hole bodies and it's entirely silent — a washer or shoulder appropriate for a 3/4 inch rod may engage only the innermost portion of a three-inch bearing face, concentrating load where it wasn't designed to go and producing readings that reflect contact geometry as much as applied force. Both faces need surfaces that cover the annulus properly.
Why do the bore suffixes skip U and X?
The series runs -P, -Q, -R, -S, -T, -V, -W, -Y, -Z, omitting U and X. Skipping visually ambiguous letters is standard practice in part numbering — U is easily confused with V, and X with Y, on a printed label, a handwritten note, or a purchase order. When ordering, use the letter exactly as it appears in the table rather than assuming the sequence is continuous, since a request for a "-U" or "-X" doesn't correspond to a product.
Can I install several THDs across one machine?
Yes, and with eighty-one configurations you can match bore and capacity to each location rather than compromising on a single part throughout. Decide early whether you need each point read individually or a combined figure, since that determines your channel count — and on a machine with several separate load paths, individual channels are usually the only way to identify which one moved. Where different configurations are in service together, particularly if some are -Y or -Z with the different nonlinearity figure, the TEDS option is a sensible safeguard against calibrations being mismatched.
How should I verify a THD that's been installed for years?
Record the unloaded zero at commissioning and treat it as your reference point — comparing against it in place is the most practical periodic check on an installed sensor, and it costs almost nothing. Beyond that, set a calibration interval and hold to it; annual is a common baseline, with more frequent verification where the reading supports a safety function or a quality record. A sensor nobody examines is exactly the one that quietly stops being trustworthy, and on a long-installed cell the drift you should worry about is the kind that develops too slowly for anyone to notice.