Set an object down and an aluminium body flexes by a few thousandths of an inch. Gauges buried in that flex report it as a resistance change, the bridge turns the change into millivolts, and a scale factor turns millivolts into kilograms. That is the whole of the electrical story.
On a single point weighing design, though, the sensor is only half of what you have built. The other half is the platform, and it is easy to think of that as a tray screwed on top rather than as part of the instrument. It is not. Whatever you fasten to the loading end becomes a structural member of the measuring chain, and it participates in the result in four separate ways.
Its own weight is applied permanently. Dead load — the mass of the platform, the tray, the bracketry and anything else always present — sits on the sensor before a single gram of the thing you actually want to weigh arrives. Standard capacity guidance is to add dead load to live load and then apply a margin on top of the total. A substantial metal platform on a modest capacity can consume a surprising share of the range, and it comes out of your overload headroom as well as your span.
Its stiffness decides where the load actually arrives. Corner compensation works on the assumption that force reaches the sensor through the mounting, in the way the geometry was shaped to handle. A platform stiff enough to behave as one piece does exactly that. A thin or unsupported one bends under an off-centre object, and a bending platform moves the effective point of application away from where the design expects it. This is the constraint that grows fastest with size: doubling a platform's span makes it far more than twice as easy to flex.
Its mass sets how quickly readings settle. A platform is a weight on a spring, and every weight on a spring oscillates before it comes to rest. On a bench scale nobody notices. On a check-weigher, a filling head or anything asked to produce a reading quickly, the platform's inertia is often what determines the cycle time — not the sensor, not the electronics.
And how it attaches decides whether the sensor works at all. The design depends on one end being held and the other free to move. A platform that touches, rests on or is fastened to both ends carries the load around the flexure rather than through it, and the readings collapse. This is the single most common assembly error on single point designs and it produces a sensor that appears almost dead rather than merely inaccurate.
All four of those matter more as the platform grows, which is what a published maximum platform size really encodes. Products built around this kind of sensor include counter and bench scales, retail checkout weighing, parcel and shipping stations, packaging and portioning equipment, pharmaceutical dispensing, laboratory balances and machinery that happens to need a weight as part of a wider process.
The bridge is conventional. What is worth understanding here is the electrical headroom this design gives you, the compensation that produces its specifications, and the two limits — one physical, one mechanical — that bound how it can be used.
Signal, and an unusually generous excitation ceiling. The bridge is 350 ohms with a rated output of 2 mV/V, and it is the same figure at every capacity in the series, so a product family sharing firmware needs only one scale factor. Nominal excitation is 10 VDC and the maximum is 20 — the highest ceiling of any load cell we publish. Because output is a ratio of what you supply, that headroom is real: run at the top and full scale is around forty millivolts rather than twenty, which is a comfortable signal for a board-level converter to work with.
The specifications come from a compensation network, not just the beam. The four-conductor wiring carries an internal temperature compensation and balance network, and that is what produces figures a bare beam could not. Nonlinearity, hysteresis and nonrepeatability are each two hundredths of one percent. Zero and span each hold to within two thousandths of a percent for every degree Fahrenheit of change, and we do not publish a tighter figure on anything else we make. And zero balance sits within one percent of rated output, so the unloaded reading is close to nominal and your front end does not need a wide input window before gain.
The first limit is the platform, and it is published in inches. Corner compensation is bounded: beyond a certain distance from centre, the moment an off-centre object applies exceeds what the machined geometry was shaped to cancel, and position sensitivity returns. That boundary is stated here as a maximum weighing platform size of 11.8 inches square. It is a hard constraint rather than a recommendation, and it cannot be bought around within the series — a larger platform needs a different architecture, not a higher capacity.
The second limit is overload, and platforms invite it. Safe overload is 150% of rated output, which sounds ample until you consider how scales are actually used. Published guidance on capacity selection notes that a weight dropped onto a scale can produce an instantaneous force of around ten times its static value. On a retail counter, a postal bench or a kitchen, things get put down heavily and occasionally dropped, so the arithmetic that matters is dead load plus live load plus a margin — commonly twenty to fifty percent — rather than live load alone.
The series comes in two body sizes. The lower capacities share one set of dimensions and the upper ones another, with a corresponding difference in weight. That is worth knowing at the design stage rather than after a housing exists: one mechanical design covers part of the range, not all of it, so a product family spanning the full span needs either two variants or a housing designed around the larger body from the outset.
Specifying a single point sensor for a weighing product is a short exercise done in an unfamiliar order, and getting the order right saves a great deal of rework. Our application engineers do this regularly and would much rather see a sketch early than a problem late.
Measure your platform before you think about weight. The size of the weighing surface is the constraint that cannot be traded against anything else, so establish it first and check it against the published maximum. If your industrial design calls for a larger surface than the sensor supports, that is a decision to take at concept stage — it changes the architecture, not the part number.
Then add up everything the sensor will carry. Live load is the heaviest thing a user will weigh. Dead load is your platform, your tray, your bracketry and anything else permanently in place. Add them, then apply a sensible margin on top of the total — twenty to fifty percent is the usual advice — and check the result against rated capacity rather than against the number on your marketing sheet.
Think about what gets dropped. If your product will be used by the public, or anywhere busy, assume things will be set down hard. That is what the overload margin is for, and it is why sizing on live load alone is optimistic. Where the risk is real, a mechanical stop under the platform is inexpensive insurance and much cheaper than warranty returns.
Check which body size your capacity falls into. The series is built on two footprints, and the change happens partway through the range. If your product family might later extend upward, designing the housing around the larger body from the start avoids re-tooling for the sake of a few millimetres.
Design the platform as a stiff, singly-attached structure. Rigid enough not to flex noticeably under an off-centre load, fastened to the loading end only, with nothing touching the fixed end or the housing at any point in its travel. Then keep its mass sensible — a heavier platform costs you capacity, settling time and nothing in return unless it is buying you stiffness.
Confirm the environment honestly. A moisture-proof sealant protects the gauge area, which suits enclosed indoor equipment — counters, benches, packaging lines, laboratory instruments. Wash-down, condensation, outdoor exposure and corrosive atmospheres are a different specification and worth raising with us before you commit rather than discovering the boundary in the field.
Then settle the electronics. With a well-behaved zero and the temperature work already done inside the sensor, feeding the bridge straight into a converter on your own board is a reasonable route. Prefer to buy that stage ready made and an amplifier signal conditioner module will hand you a voltage or current output, while a digital display pays for itself on the bench while the design is still moving. Cal-Teds plug and play supplies a connector carrying an IEEE 1451.4 TEDS memory, so a compatible instrument reads the sensor's calibration data instead of somebody typing it in.
Send us the platform dimensions, the heaviest item to be weighed, the weight of your own structure and a note on how the product will be handled, and we will confirm the capacity and body size that suit. Stock holding covers the full capacity list, and academic and research purchases are discounted — ask when you enquire.
ESP Series Load Cell Applications.
The Transducer Techniques ESP Series economical single point bending beam load cells suit OEM force measurement applications, particularly electronic scales and weighing machines.
- Electronic Scales: ESP Series load cells are used in electronic scales of all kinds, including kitchen, bathroom and industrial scales.
- Weighing Machines: These load cells are used in weighing machines across industrial and commercial settings.
- Retail Point of Sale Systems: ESP Series load cells are integrated into checkout counters and point of sale weighing equipment.
- Parcel and Package Weighing: These load cells are used in parcel, package and shipping weighing systems.
- Food Processing and Packaging: ESP Series load cells provide weight measurement in food processing and packaging operations.
- Pharmaceutical Manufacturing: These load cells are used for measurement and quality control in pharmaceutical manufacturing.
- Laboratory Balances: ESP Series load cells are used in laboratory balances for research and analytical work.
- Material Testing: These load cells are used in material testing applications.
- Customized Scales: ESP Series load cells are integrated into customized scales and weighing systems.
- Quality Control: These load cells are used for product verification in quality control operations.
- Production Force Monitoring: ESP Series load cells provide force monitoring in production processes.
- Load Monitoring: These load cells are used for load monitoring in conveyor systems and elevators.
The Transducer Techniques ESP Series combination of affordability, high accuracy and resistance to eccentric loading delivers value across industrial, commercial and specialized measurement applications.
Frequently Asked Questions
What capacities does the ESP Series cover?
Seven, specified in kilograms: ESP-6 at 6 kg (13 lb), ESP-10 at 10 kg (22 lb), ESP-15 at 15 kg (33 lb), ESP-20 at 20 kg (44 lb), ESP-25 at 25 kg (55 lb), ESP-30 at 30 kg (66 lb) and ESP-35 at 35 kg (77 lb). The range is built on two body sizes, with the change occurring between the 20 and 25 kg models — the lower four share one footprint and weigh 7.1 oz, the upper three share a larger one and weigh 9.2 oz. Worth checking before a housing is designed.
What is the maximum platform size for an ESP?
11.8 inches square, which is 300 mm each way. That figure is the practical boundary of the corner compensation: beyond it, the moment an object applies near the edge exceeds what the machined geometry can cancel, and the reading starts to depend on where the object sits. It is a hard limit rather than a guideline, and it cannot be solved by choosing a higher capacity — a larger weighing surface needs a different approach entirely. Check your platform against it before anything else.
How accurate is the ESP Series?
Nonlinearity, hysteresis and nonrepeatability are each 0.02% of rated output, and the temperature coefficients are 0.002% per °F on both zero and output. Those temperature figures are the tightest we publish on any load cell in the catalogue. They are not a property of the beam alone — the four-conductor wiring includes an internal temperature compensation and balance network, and that is what turns a machined aluminium body into a part that behaves predictably across temperature and from one unit to the next.
What is the rated output and excitation?
2 mV/V nominal from a 350 ohm bridge, and the same figure at every capacity in the series — so a product family spanning several ranges needs only one scale factor in firmware. Nominal excitation is 10 VDC with a maximum of 20 VDC, the highest ceiling of any load cell we publish. Output is proportional to excitation, so running toward the top gives roughly forty millivolts at full scale instead of twenty, which is a comfortable signal for a converter on your own board.
Does the weight of my platform count against the capacity?
Yes, and it is the most commonly missed step in sizing. The platform, tray, bracketry and anything permanently attached is dead load, applied to the sensor continuously. Standard capacity guidance is to add dead load to live load and then apply a margin on top — commonly twenty to fifty percent — before comparing the total against rated capacity. A heavy metal platform on a modest range can eat a meaningful fraction of the sensor before the user puts anything on it, and it takes that share out of your overload headroom too.
How should the platform be attached?
To the loading end only, and to nothing else. A single point cell works because one end is held rigidly and the other is free to deflect; anything that connects the platform to the fixed end, the housing or the base carries load around the flexure instead of through it. Fix the mounting end to a rigid, flat structure, keep fastener torque sensible in an aluminium body, and confirm that nothing touches at full deflection as well as at rest — a platform that clears at zero and fouls at full load produces a reading that goes non-linear at exactly the wrong moment.
How stiff does the platform need to be?
Stiff enough that it does not visibly flex under an off-centre load. Corner compensation assumes force reaches the sensor through the mounting in a predictable way, and a platform that bends under a weight placed near its edge moves the effective point of application away from where the geometry expects it. This matters more the larger the platform gets, so a surface approaching the maximum size deserves ribbing, a thicker section or a supporting frame rather than a plain sheet. It is a cheap thing to get right at the design stage and awkward to fix afterwards.
What environmental protection does the ESP have?
A moisture-proof sealant over the gauge area, with a compensated temperature range running from below freezing to just above forty Celsius and a safe range extending further. That combination suits enclosed indoor equipment — retail counters, laboratory benches, packaging machinery, postal equipment — and copes with cool rooms and unheated spaces better than an industrial sensor compensated only around room temperature. It is not a sealed or hermetic specification, so wash-down, condensing environments and outdoor exposure should be described to us rather than assumed.
What is the TEDS option?
It supplies the sensor with an AD9 connector carrying a TEDS memory to IEEE 1451.4, holding the unit's own calibration data so a compatible smart instrument reads it automatically rather than relying on someone entering constants correctly. The value is highest where sensors move between products or rigs — a development bench running several capacities, a service operation swapping units, or a production test station where a wrong scale factor would pass unnoticed. In a single fixed installation it earns less.
How does the ESP compare with your lower capacity single point cells?
They work on the same principle and share the same accuracy class; the differences are scale and headroom. The ESP covers 6 to 35 kg against 1 to 10 kg, supports a platform half again as large in each direction, gives a higher and constant rated output across its range, and accepts a higher maximum excitation. The lower capacity series has the advantage of a single footprint across every model. Choose primarily on platform size and weight range, and tell us both — the answer is usually obvious once those two numbers are on the table.
Questions From The Field
My scale reads high when the object is near the edge of the platform.
Three things to check, in order. First the platform size against the published maximum — a surface larger than the compensation was designed for will do exactly this. Second the platform's stiffness: if it visibly bends when a weight sits near a corner, the load is no longer arriving where the geometry assumes, and the fix is a stiffer platform rather than a different sensor. Third the mounting, since a base that flexes under load has much the same effect. A genuinely faulty sensor is a distant fourth on this list.
The reading barely changes when I put weight on.
Something is almost certainly bridging both ends of the sensor. The design needs one end fixed and the other free; if the platform, a bracket, a fastener or even a stiff cable connects across both, most of the load takes that path instead of going through the flexure. Look for anything touching both halves, and check at full deflection rather than only at rest — a clearance that exists unloaded can disappear under weight. The other frequent cause is a platform catching on the housing somewhere around its edge.
Readings take several seconds to settle. Is that normal?
It is a consequence of your platform rather than the sensor. A weighing platform is a mass on a spring, and the heavier it is the longer it oscillates before coming to rest. On a bench scale nobody minds; on a check-weigher or a filling head it sets your cycle time. If you need faster readings, reducing platform mass helps more than anything you can do in software, though filtering in firmware will trade settling time against noise if the mechanical route is closed. Also check that nothing in the assembly is rubbing, since friction produces a slow creep toward the true value that looks very similar.
Something heavy was dropped on the scale. Should I be worried?
Possibly, because impact and static weight are very different things. Published capacity guidance notes that a dropped weight can produce an instantaneous force of around ten times its static value, which will pass 150% of rated output easily. Check the unloaded reading against the zero balance figure once the platform is removed — a zero that has shifted well outside specification and stayed there indicates permanent set. Then confirm a known weight still reads correctly, because a beam can return to an acceptable zero and still have lost span. On products the public handles, a mechanical stop under the platform is worth designing in.
Do I need to calibrate every unit I build?
You need a tare on every unit without exception, and it removes your platform's dead weight as well as any sensor offset. Span calibration is a judgement. The accuracy and temperature specifications here are tight enough that a product needing a repeatable indication rather than a stated weight can often work from nominal figures. Where the display shows a weight a customer acts on, calibrate each assembled product against a known mass — that captures your platform, your mounting and your electronics as well as the sensor, and it is the combination your user actually experiences.
My zero drifts slowly over the first few minutes after power-up.
Usually thermal settling in your product rather than the sensor. Electronics inside a closed housing warm the air around them, and although the temperature coefficients on this part are the tightest we publish, a warming enclosure with a metal platform on top will move the zero a little while everything equalises. Take the tare once the product has reached working temperature rather than immediately at switch-on, and consider a slow automatic re-zero for equipment left running unattended. If the drift persists well past warm-up, look for something creeping mechanically instead.
Can I run the sensor at a higher excitation to get more signal?
Yes — up to the 20 VDC maximum, which is the most generous ceiling of any load cell we publish. Output is a ratio of excitation, so doubling the supply doubles the signal, and at the top of the range you have roughly forty millivolts of full scale to work with. Two cautions. Do not exceed the maximum. And make sure the instrument or converter knows what voltage it is supplying, since a front end still scaled for 10 volts will read double. Settling on one excitation voltage and calibrating at it is the tidy approach.
How do I choose between two capacities when my weight range sits between them?
Work from the total rather than the live load. Add your platform and fixture weight to the heaviest item you need to weigh, apply a margin for careless handling, and see which capacity contains the result. If that lands you awkwardly at a boundary, two things tip the decision: whether your product is likely to be loaded roughly, which argues for the larger capacity, and whether resolution at the bottom of the range matters, which argues for the smaller. Also check which body size each option uses, since that may settle it for you on mechanical grounds alone.