A load cell is a sensor that turns applied force into an electrical signal. Strain gauges bonded to a machined metal element register the minute deformation the force produces, and a bridge circuit converts that into a voltage proportional to the load. That much is common to every load cell ever built.
What varies enormously is how the force is expected to get into the sensor. Some designs are threaded at both ends and carry load in a straight line through the body. Some bolt to a flange. Some have a hole through the middle for a bolt or shaft. And compression-only designs simply present a face and wait to be pressed against — no threads carrying the measured load, no attachment at all in the load path, just surface meeting surface.
That last category is worth understanding on its own terms, because a compression-only cell hands part of the measurement job to you. With a threaded sensor, the load path is defined by the hardware. With a compression cell, the load path is defined by whatever is pressing on it, how flat and hard that thing is, and how well centered it happens to be. The sensor can be superb and the measurement still poor if the mechanical interface isn't right.
Sub-miniature compression cells push this further by shrinking the whole thing into a package that can be a fraction of an inch across. At that size the sensing element is machined from high-strength material — commonly a precipitation-hardening stainless such as 17-4 PH, heat treated for strength and dimensional stability — because there simply isn't enough cross-section to make up for a weaker alloy. A loading face barely wider than a pencil eraser still has to carry hundreds of pounds without yielding.
Across the wider category you'll find compression-only designs, tension-only designs, universal cells that read both directions, S-beam types for in-line push and pull, bending and shear beams in scales and conveyors, low profile and pancake formats where height is limited, through-hole and load washer types that let a bolt pass through, and button or load button types for tight compression fits. Compact compression sensors in particular turn up in materials testing, automotive and aerospace component testing, medical device verification, biomechanics research, and any test fixture where there's a load path but almost no room.
Two things have to go right for a load cell to give you a number you can trust: the electrical chain, and the mechanical one. The electrical side is well behaved and rarely surprises anyone. The mechanical side is where most disappointing data actually comes from.
The electrical chain starts with excitation. A load cell produces no signal on its own — it modulates a voltage you supply across its bridge. Sensitivity is quoted in millivolts per volt for exactly this reason: a 2 mV/V sensor excited at 10 VDC delivers roughly 20 mV at full capacity, and the same sensor excited at 5 VDC delivers roughly 10 mV. Neither is wrong, but the two are not interchangeable. Excitation used in service must match the excitation the sensor was calibrated at, or every reading is scaled incorrectly.
Excitation ratings are not universal. Not every load cell is rated for 10 VDC, and smaller sensing elements are often specified lower. A compact element has less material to dissipate the heat that excitation current generates in the gauges, and that self-heating shows up as drift. Where a manufacturer specifies a reduced excitation for particular capacities within a series, it isn't a suggestion — it's a limit set by the physics of that specific element.
Strain becomes signal. Applied force deflects the sensing element by thousandths of an inch. Bonded gauges deform with it, resistance shifts, the bridge unbalances, and a proportional millivolt output appears. Amplification, filtering, digitizing, and the stored calibration turn that into engineering units.
The mechanical chain is where compression cells earn their reputation. A compression sensor reads what its loading face experiences, which means the face doing the pressing is functionally part of the instrument. Three things about that surface matter more than most people expect:
Flatness. A mating surface that isn't flat changes where contact occurs as load increases. Testing has shown non-flat contact surfaces can roughly triple repeatability error and increase rotational error several times over.
Hardness. A soft platen indents under load, so the force path changes partway through the test and the sensor seats slightly differently every cycle. Documented output shifts of around 0.3% have been attributed purely to changing platen material or hardness.
Centering. Compression button designs are notably sensitive to being loaded off-center, and the resulting cosine error is not small — without proper alignment hardware, errors ranging from 1% to 10% of rated output have been documented, while adding alignment adapters has been shown to improve reproducibility dramatically.
The lesson is a simple one: if the mechanical interface isn't repeatable, the measurement won't be either, no matter what the sensor's specification sheet claims.
Specifying a compact compression load cell is a slightly different exercise from specifying a general-purpose one, because the constraints usually arrive in a different order. Space comes first, the load path comes second, and the sensor almost picks itself once those two are settled. Our application engineers work through this daily, so a phone call early is usually cheaper than a redesign later.
Start with the envelope. How much room do you actually have — diameter and height both? Sub-miniature compression cells exist precisely because designers run out of space, and the smallest units are a fraction of an inch in each dimension. Knowing your real clearance narrows the field faster than any other single question.
Then define the load path. What will press on the sensor, and what is that thing made of? Can you guarantee it stays centered? Is the mating face flat, hard, and stable, or is it a machined surface that might dish over time? If you can't answer these confidently, budget for a hardened platen or an alignment adapter as part of the installation rather than treating them as accessories.
Size the capacity honestly. Pick a capacity so your working force sits well within range for good resolution, then check your genuine worst case against the safe overload rating. Compression fixtures have a habit of delivering more force than intended during setup, so a mechanical hard stop is worth designing in.
Check the excitation requirement per capacity. Don't assume every model in a series runs at the same excitation voltage. Confirm the requirement for the specific capacity you're ordering and set your instrument to match, because a mismatch between calibration excitation and service excitation produces a scaling error that looks exactly like a bad sensor.
Decide what direction you actually load in. Compression-only designs are calibrated in compression as standard. If your application has any tension component, say so up front rather than assuming a compression calibration will cover it.
Account for the environment. Note the compensated temperature range, within which published accuracy holds, and the zero and output drift coefficients, which let you estimate error across a known temperature swing rather than guessing. Stainless construction helps in humid or mildly corrosive settings; for sustained outdoor, marine, or submerged use, ask about a hermetically sealed cell.
Plan the readout. A precision power supply, an amplifier signal conditioner module, or a digital display with alarms, analog output, or data logging — and Cal-Teds plug and play if the sensor will move between instruments and you'd rather not re-enter calibration data each time.
Tell us your available space, expected force, what the mating surface is made of, and how the load arrives, and we'll help you land on the right sensor. Standard products ship next day from stock, and educational discounts are available.
SLB Series Load Cell Applications.
The Transducer Techniques SLB Series load cell, a sub-miniature load button load cell made from heat-treated 17-4 PH stainless steel, is designed for precise force measurement in various applications where space constraints and high accuracy are critical.
- Material Testing: The SLB Series load cell is commonly used in materials testing machines for measuring tensile and compressive forces in materials like metals, plastics, and composites. It is crucial for determining material properties and quality control.
- Product Testing and Quality Control: Manufacturers use SLB Series load cells to ensure that products meet specific force or weight requirements during production. This is common in industries such as electronics, consumer goods, and automotive manufacturing.
- Automotive Component Testing: The load cell is employed to test various automotive components, including switches, pedals, seatbelts, and airbags, to ensure they meet safety and performance standards in the automotive industry.
- Aerospace and Aviation: In the aerospace sector, the SLB Series load cell is used to measure forces and loads in small components, such as control surfaces, actuators, and mechanisms, contributing to the safety and performance assessment of aircraft and spacecraft.
- Biomechanics Research: Researchers use SLB Series load cells in biomechanics studies to measure forces and pressures on the human body during activities like walking, running, and sports. This data aids in designing ergonomic products and improving athletic performance.
- Product Development: Engineers and designers use SLB Series load cells during the development and testing of various products, including handheld tools, consumer electronics, and mechanical components, to assess the forces applied during normal operation.
- Educational Laboratories: Educational institutions incorporate SLB Series load cells into physics and engineering laboratories for teaching students about force measurement principles and conducting hands-on experiments related to mechanics and materials science.
- Medical Devices: SLB Series load cells are utilized in the medical device industry for testing medical equipment and devices, such as syringes, infusion pumps, and surgical instruments, to ensure they meet force and performance specifications.
- Small-Scale Manufacturing: Industries like jewelry making and watch manufacturing use SLB Series load cells to ensure precise assembly and quality control of small components.
- Custom Machinery: Manufacturers and research facilities integrate SLB Series load cells into custom-built machinery and equipment for specialized testing and manufacturing processes that require precise force measurement and control.
- Customized Force Measurement: The SLB Series load cell can be adapted and customized for specific applications and industries where sub-miniature force measurement is required, such as in the development of specialized sensors and research equipment.
The Transducer Techniques SLB Series load cell's compact size, high accuracy, and durable construction make it a valuable tool in industries and research fields that demand accurate force measurement in small-scale or precision applications.
Frequently Asked Questions
What is the SLB Series, and what capacities does it come in?
The SLB Series is our sub-miniature load button compression load cell, built for applications where there is a real load path but almost no room to put a sensor in it. It's offered in seven capacities — 25, 50, 100, 250, 500, 750, and 1,000 lb — all at the same price point, so you can select purely on the force you need to measure rather than weighing capacity against cost.
Why do the SLB-25 and SLB-50 use 5 VDC excitation when the rest of the series uses 10 VDC?
This is the single most important spec to catch on this series. The SLB-25 and SLB-50 are rated for 5 VDC excitation; the SLB-100 and above run at 10 VDC. The reason is thermal: the smallest sensing elements have very little material to carry away the heat that excitation current generates in the strain gauges, and that self-heating shows up as drift. The lower rating isn't a recommendation, it's a limit set by the physics of that particular element — so set your instrument to match the specific capacity you ordered, not to a series-wide default.
Why is the entire SLB Series made from heat-treated 17-4 PH stainless steel?
At this size there's no room for a compromise material. 17-4 PH is a precipitation-hardening stainless: heat treatment forms fine particles within the metal structure that raise its strength dramatically without the distortion that would ruin a precision part. The result is a material several times stronger than standard stainless with good corrosion resistance, which is what lets a loading face barely wider than a pencil eraser carry a thousand pounds without yielding. Unlike series that switch materials as capacity climbs, every SLB uses it.
How physically small is an SLB load cell?
Small enough to change what's possible in a cramped fixture — the SLB-25 and SLB-50 measure roughly 0.375 inches in diameter and 0.250 inches in height, with dimensions stepping up modestly through the higher capacities. Check the dimensional table for the exact diameter and height of the capacity you need before committing your fixture design, since the difference between capacities can matter when you're working with this little clearance.
What does 0.002 inches of deflection at rated output mean in practice?
It means the SLB barely moves under load — two thousandths of an inch at full capacity, which is the lowest deflection across our miniature range. Practically, that keeps your fixture geometry essentially unchanged between no load and full load, which matters when the sensor is sandwiched into a stack-up with tight clearances. Low deflection also means high stiffness, so the sensor settles quickly rather than continuing to move as load is applied.
What accuracy can I expect from the SLB Series?
Nonlinearity and hysteresis are each specified at 0.25% of rated output, nonrepeatability at 0.1% of rated output, and zero balance at 2.0% of rated output. Those figures are looser than our threaded miniature series, and that's an honest consequence of the form factor: a compression button transmits load through a contact surface rather than through fixed threaded hardware, so some measurement variability comes from the interface itself. In exchange you get a sensor that fits where nothing else will. If your application needs tighter linearity and you have room for a threaded cell, that's worth a conversation.
Why does the surface pressing on an SLB need to be flat?
Because on a compression-only sensor, the surface doing the pressing is effectively part of the instrument. The SLB's loading diameter is slightly convex specifically to distribute load predictably, but that only works if it meets a flat mating face. If the mating surface is dished, tilted, or worn, the contact point shifts as load increases, and your readings shift with it. Getting that surface right is not a detail — it's a prerequisite for the accuracy on the datasheet.
Is the SLB compression only, or can it be calibrated for tension?
The SLB is a compression load cell and ships with compression calibration as standard, which covers the overwhelming majority of button-cell applications. Tension calibration is available as an option if your application requires it. Specify it at order time rather than assuming a compression calibration will transfer, since the load path and therefore the calibration relationship differ between the two directions.
How much does temperature affect an SLB reading?
The SLB is temperature-compensated from 60° to 160°F, with a safe operating range of −65° to 200°F. Within the compensated band, output drifts 0.005% of load per °F and zero drifts 0.01% of rated output per °F. That zero coefficient is worth noting — it's twice the figure on some of our threaded miniature series, so on a long test in a warming room it's the zero, not the span, that will move first.
Can I get the SLB with the plug-and-play TEDS option?
Yes — OPT-TEDS is available on the SLB Series. It stores the sensor's calibration data in a chip on the connector, so a compatible display or conditioner reads it and configures itself automatically instead of requiring manual entry. Given that excitation and calibration differ across SLB capacities, this is genuinely useful if you'll be swapping different SLB units through the same instrument, since it removes a step where mistakes tend to happen.
Questions From The Field
I connected 10 VDC to an SLB-25 by mistake — what should I do?
Disconnect it and reset your instrument to 5 VDC first. Two separate things have gone wrong: every reading taken at the wrong excitation is scaled incorrectly, so that data isn't salvageable by adjustment after the fact, and the element may have been self-heating the whole time, which shows up as drift that can persist while it cools. Once you're back at the correct excitation, let it stabilize, re-zero, and check it against a known load. If the zero won't settle where it used to, contact us about having it checked.
My SLB readings won't repeat when I take the fixture apart and put it back together.
This is the classic compression-button symptom, and it's almost always the mechanical interface rather than the sensor. If the mating surface isn't flat, contact happens in a slightly different place each time you reassemble, and repeatability collapses — testing has shown non-flat contact surfaces can roughly triple repeatability error. Check that the loading face is genuinely flat and unworn, that the sensor seats the same way every time, and that nothing in the stack-up shifts as you tighten it down. A dedicated, repeatable seat for the cell fixes this more reliably than careful assembly technique does.
What should the platen or loading block pressing on my SLB be made of?
Use something hardened, flat, and dimensionally stable. A soft platen indents under load, which means the force path changes partway through your test and the sensor seats differently on every cycle — documented output shifts of around 0.3% have been traced purely to a change in platen material or hardness. Aluminum or mild steel loading blocks are a common and avoidable source of error here. Hardened steel is the safer default.
Why is my SLB reading lower than the force I know I'm applying?
Off-center loading is the usual culprit. A compression button reads the component of force along its axis, so a load that arrives even slightly off-center or at an angle gets under-reported through cosine error — and button designs are unusually sensitive to this. Documented errors in the absence of proper alignment hardware have ranged from 1% to as much as 10% of rated output, while adding a proper alignment adapter has been shown to improve reproducibility dramatically. Before suspecting calibration, verify the load is genuinely centered on the button.
My SLB reading creeps downward while I hold a steady load. Is the sensor failing?
Probably not. On a compression setup, a slow drift during a sustained hold often comes from the interface continuing to settle — surfaces bedding in, a soft platen slowly indenting, or a fixture relaxing under sustained load. Temperature is the other candidate; at 0.01% of rated output per °F of zero drift, a room that warms noticeably over a long hold will move your reading. Check the mechanical explanation first by holding the same load against a hardened, flat surface and seeing whether the creep persists.
Can I recess an SLB into a pocket or counterbore in my fixture?
Often yes, and it's a good way to locate the cell repeatably, but the pocket has to be machined so that only the loading button contacts the pressing surface. If the fixture bottoms out on the sensor body, or the pocket walls pinch it, part of your load bypasses the sensing element and your reading will be low and inconsistent. Make the pocket depth and diameter deliberately, using the dimensions for your specific capacity, and confirm free clearance around the body before you load it.
When should I choose an SLB instead of a threaded miniature load cell?
Choose the SLB when space genuinely dictates it and your loading is compression only — that's what it's built for, and nothing threaded will fit the same envelope. Choose a threaded miniature cell when you need tighter linearity and hysteresis, when your application has any tension component, or when you can't guarantee a flat, hard, well-centered mating surface. The SLB's specifications assume a good mechanical interface; if you can't provide one, a design that carries load through threads will serve you better.
Do I need to change my instrument setup when I swap between different SLB capacities?
Yes, and in two ways. First, excitation — moving between an SLB-50 and an SLB-100 means moving between 5 VDC and 10 VDC, and getting that wrong scales every reading. Second, the calibration values for the specific serial number you've installed. If you routinely swap capacities through one instrument, the OPT-TEDS option is worth having, since the sensor carries its own calibration data and the instrument configures itself rather than relying on someone remembering which unit is fitted.