Every bridge sensor needs something standing between it and the equipment that will use its measurement, and a load cell signal conditioner is that something. It supplies excitation, amplifies the few thousandths of a volt that come back, filters what you do not want, and delivers a voltage or a current that a controller, a data acquisition card or a display can accept.
The specification tells you what a board can do. It does not tell you what owning one is like. And on this board the difference between the two is the whole point, because what distinguishes the LCA-RTC is not its electrical performance — it is that its terminals accept bare wire, and that the terminal blocks come off.
Consider what those two facts actually change.
No soldering means a different person can install it. A board that terminates in connectors somebody has to solder is fitted by an instrumentation technician in a workshop, with a bench, an iron and time. A board that takes bare wire into screw clamps is fitted by whoever is already standing in the panel with a screwdriver. That is not a small distinction on a Tuesday morning when a line is down and the person who owns the soldering iron is at another site.
Removable is the word that matters more, and it is easy to read past. A fixed screw terminal still means unlanding every wire to change the board and landing them all again afterwards, correctly, from a drawing, in whatever light the panel offers. A removable block comes off with the field wiring still clamped in it. You unplug it, swap the board, plug it back on. The field wiring is never disturbed, so it cannot be reconnected wrongly — which removes not just the labour but the most likely way a straightforward replacement turns into a fault-finding exercise.
That is also why a replacement terminal block is offered as a stocked item rather than a spare part. The block is treated as something you might want two of: one on the machine, one made up on the bench and ready to go.
The rest of the board is built with the same intent. The supply is protected against reverse polarity down to minus forty volts — well beyond anything a twenty-four volt panel could do to it — so landing the supply backwards costs you the time to notice, and nothing else. Everything that has to be set is set with jumpers and screwdriver-adjustable potentiometers rather than software, which means the configuration is visible, does not require a laptop, and cannot be lost.
None of that is glamorous, and all of it is what decides the true cost of the installation. The purchase price is a known number arrived at once. Commissioning time, downtime and the chance of a rewiring error recur for as long as the machine runs, and a board that swaps in two minutes without touching the field wiring is a different proposition over ten years from one that does not.
Excite, amplify, filter, output. Each stage has a setting, and the useful thing is knowing what each specification is really telling you.
The filter is two-pole, and that describes its character rather than just its corner. Six settings are available, from a hundred hertz up to thirty kilohertz. Two poles means the response falls away at twelve decibels per octave beyond the corner — a gentle, well-behaved slope rather than a wall. That is the right shape for measurement, because steep filters distort the shape of a signal near the corner in ways that matter when you are looking at a waveform rather than a number. But it also means content well above your setting is reduced rather than removed, so a filter alone will not eliminate a specific interfering frequency; it will only make it smaller.
The steps are spaced about three to one, which is more thoughtful than it looks. A hundred hertz, three hundred, one kilohertz, three, ten, thirty. Whatever your measurement actually contains, there is a setting within roughly a factor of two of the ideal, which is close enough that the choice is rarely agonising. Pick the lowest one that still passes what you are trying to measure.
Note that the corner is quoted at minus six decibels. Most manufacturers quote the minus three decibel point, which sits higher up the curve, so the two figures are not directly comparable. A setting labelled ten kilohertz here has its conventional minus three decibel corner somewhat below ten kilohertz. This is not a shortfall — it is a more conservative way of stating the same filter — but it is worth allowing for when your signal's frequency content sits close to a setting, and worth knowing when comparing this board against someone else's number.
Temperature stability is published, and it is the specification that decides whether readings agree across a season. Zero and span each move by no more than three thousandths of one percent of full scale per degree Celsius. Put a real number on that: a thirty degree swing between a cold morning and a warm afternoon in an unventilated cabinet moves each of them by around nine hundredths of one percent of full scale. Compare that against the load cells it will be reading, most of which drift several times faster than the board does, and the conclusion is the useful one — if your installation drifts with temperature, the conditioner is very unlikely to be the reason. Look at the sensor, the fixture and the structure first.
Linearity error through this board is quoted at 0.005 percent of full scale at worst. That is roughly six times better than a very good load cell manages, which is exactly the relationship you want from the part in the middle: invisible in the error budget, so that when something reads wrong you can concentrate on the mechanics.
Excitation is five or ten volts, into a minimum load of 350 ohms. That minimum is really a statement about quantity: it permits a single standard bridge and no more. Two of them in parallel present half that and are outside the specification, so several sensors means several boards — which is usually the better arrangement anyway, since independent channels do not interact and each can be set up for its own sensor.
Output is jumper-selectable between voltage and current. Two bipolar voltage ranges, so tension and compression or clockwise and counterclockwise arrive as positive and negative without anything extra, and three current ranges including 4–20 milliamps. The choice is about the receiving end and the distance rather than about preference, and because it is a jumper rather than a factory option, changing your mind later costs nothing.
And there is a shunt calibration facility for checking the chain without loading the sensor. A precision resistor switched across the bridge unbalances it by a known amount and produces a predictable output, so the sensor, the cable, the board and everything downstream can all be confirmed still working. Sockets are provided for a resistor of your own if you would rather check at a value that suits your particular sensor.
Choosing between conditioners is usually a question of where the board lives and who has to look after it. Our applications engineers would rather talk through the whole installation than the board alone.
Decide first who is going to wire it and who is going to maintain it. If the board is going inside a product you manufacture, in volume, with a cable loom made up as part of your own assembly, soldered connectors are a perfectly sensible arrangement and there is a version for that. If it is going into a control panel, into one machine, to be looked after by whoever is on shift, then screw terminals that come off as a block are worth more than any specification on the sheet. Be honest about which situation you are actually in, because it is easy to specify for the day of installation and forget the following ten years.
Then work out how fast your measurement is. Weighing, load holding and slow proof loading live at the bottom of the filter range. Presses, actuators and machine cycles sit in the middle. Impacts, drops and structural events need the top. Choose the lowest setting that still passes what you are measuring — a wider setting than you need admits noise you did not have to accept.
Let the destination decide the output format, and let the cable length decide it again. Voltage where the acquisition hardware is close and expects a voltage. Current once the run gets long, once the route is shared with anything carrying power, or once the destination is a controller that thinks in milliamps. Of everything the board can produce, a 4–20 milliamp loop survives a long cable best — and reaching it means moving a jumper, not ordering a different board.
Plan the enclosure, because the board does not provide one. This is a small plastic-cased component intended to live inside something else — a control panel, a machine, a junction enclosure. It carries no ingress rating of its own, so whatever surrounds it is what protects it. A DIN rail clip is available so it can sit alongside other control components in a standard cabinet, which is how most installations end up.
Check the temperature where it will actually sit. Full performance is specified from freezing to fifty-five degrees Celsius, with derated operation across a much wider band. Ordinary panels sit well within it. What catches people out is the enclosure that makes its own heat — sunlight on a sealed door, a neighbouring process, or a cabinet crowded with drives — where the internal air can be many degrees above the room. Measure rather than assume.
Put a spare terminal block on the same purchase order. This is the cheapest insurance in the catalogue. A spare block, wired up and labelled on the bench, turns a future board replacement into a two minute job with no wiring decisions in it at all. Buying it later, in a hurry, is how a five minute swap becomes an afternoon.
Take the accessories seriously. A trim pot tool sounds trivial until somebody adjusts a multi-turn potentiometer with the wrong screwdriver and damages it. Where a panel offers no low voltage rail at all, the plug-in adapter solves that in one part rather than in a design change. Neither is expensive and both prevent the specific problems they exist for.
Give us four things — the sensor you are using, the speed of the event, the signal your equipment expects, and who will be looking after the panel afterwards — and we will confirm both the configuration and which version of the board suits you.
LCA-RTC Load Cell Signal Conditioner Applications.
The Transducer Techniques LCA-RTC provides low cost dedicated signal conditioning for a single bridge type load cell or torque sensor, with removable screw-clamp terminal connectors that accept wires without soldering, jumper-selectable sensitivity and filtering, and a choice of voltage or current outputs.
- Control Panel Installation: Screw-clamp terminals and a DIN rail clip allow the board to be fitted and maintained by panel electricians using ordinary tools.
- Retrofit and Upgrade: Bare wire termination suits replacing an older conditioner in an existing installation without remaking cable assemblies.
- Machine Force Monitoring: Continuous conditioning of a load cell built into production equipment, powered from the machine's own DC control supply.
- PLC and Controller Interfacing: Jumper-selectable 4–20 mA output delivers a process signal to a plant controller with no separate transmitter.
- Data Acquisition: Bipolar voltage outputs at ±5 V or ±10 V match common acquisition card ranges and report direction as well as magnitude.
- Dynamic and Impact Testing: Filter settings up to 30 kHz pass fast events that a weighing instrument would remove before they could be recorded.
- Static Weighing and Load Holding: The lowest filter settings give the quietest possible output where the measurement changes slowly.
- Torque Sensor Conditioning: The same board conditions bridge type torque sensors, with sensitivity and gain set to suit the unit.
- Field Verification: Shunt calibration confirms that sensor, cable, conditioner and readout are all intact without applying a physical load.
- Multi-Sensor Systems: One board per sensor gives independent channels that can be set up individually and replaced without disturbing the others.
The LCA-RTC works with our full range of load cells and torque sensors, and is supported by mains adapter, DIN rail clip, replacement terminal block and trim pot tool accessories.
Frequently Asked Questions
What is the LCA-RTC and how does it connect to my wiring?
It is dedicated signal conditioning for a single bridge type load cell or torque sensor, connected through removable screw-clamp terminal connectors that accept wires without soldering. That termination is the defining feature: bare conductors go straight into the clamps, and the blocks unplug from the board with the wiring still landed in them. Electrically it does what a conditioner does — excites the bridge, amplifies the millivolt signal, filters it and delivers a voltage or current output — but the way it connects is what decides whether it suits your installation.
What does "removable" mean on a terminal block, and why does it matter?
It means the part holding your wires separates from the part carrying the electronics. With a fixed terminal, changing the board means loosening every conductor, taking them out, and putting them all back on the new one in the right order. With a removable block you unplug it, complete with the wiring, and plug it onto the replacement. The labour saving is real but the more valuable part is that the field wiring is never disturbed and therefore cannot be reconnected incorrectly. That is the difference between a board swap that takes minutes and one that turns into fault-finding.
What filter settings are available, and how sharply do they roll off?
Six two-pole low-pass settings, from a hundred hertz through three hundred, one kilohertz, three, ten and thirty. Two poles gives a roll-off of twelve decibels per octave — gentle, well behaved and appropriate for measurement, since very steep filters distort the shape of a signal near their corner. The steps are spaced roughly three to one, so whatever your measurement contains there is a setting within about a factor of two of ideal. The rule is to select the lowest setting that still passes the frequency content you actually need, because anything wider simply admits noise you had no reason to accept.
Why is the filter corner quoted at −6 dB?
Because it is a more conservative way of stating the same filter, and it matters when you compare specifications. The convention across most of the industry is to quote the frequency at which the response has fallen by three decibels. A minus six decibel point sits further down the slope, so the conventional minus three decibel corner of any given setting here is somewhat below the number printed on it. Nothing is being lost — it is the same filter described differently — but if you are comparing this board against another manufacturer's figure, or if your signal's frequency content sits close to a setting, make sure you are comparing like with like and allow a little margin.
How much does temperature move the reading?
Zero and span each shift by no more than 0.003 percent of full scale per degree Celsius. In practical terms, a thirty degree swing between a cold morning and a warm afternoon in a cabinet moves each of them by roughly nine hundredths of one percent of full scale. That is a good figure, and the useful comparison is against the sensor rather than in isolation: most load cells drift several times faster than this board does. So if your installation reads differently at different times of day or year, the conditioner is unlikely to be the cause, and the sensor, the mounting and the structure are the places to look.
What happens if the supply is connected backwards?
Nothing damaging. The board is protected against reverse polarity down to minus forty volts, which is well beyond anything a twenty-four volt control supply could inflict on it. Since the board normally runs on anything from about twelve to twenty-six volts, that protection covers a comfortable margin either side of any plausible mistake. It will not work until the connection is corrected, but a miswiring during commissioning costs you the time to spot it and nothing more — which on a panel being wired against a deadline is worth having.
What output and excitation options are there?
Output is jumper-selectable between two bipolar voltage ranges — up to five or ten volts either side of zero — and three current ranges, including 4–20 mA. The bipolar ranges mean tension and compression, or clockwise and counterclockwise, arrive as positive and negative without anything additional. Excitation is five or ten volts into a minimum load of 350 ohms, delivering up to thirty milliamps. Because both are jumpers rather than factory-set options, an installation whose requirements change does not need a different part number.
How can I verify the installation without loading the sensor?
Use the shunt calibration facility. A precision resistor is switched across the bridge, unbalancing it by a known amount and producing a predictable output, which confirms in one action that the sensor, the cable, the conditioner and everything downstream are all still doing what they did at commissioning. That matters most where applying a real load is difficult — a sensor built into a machine, a vessel in service, a rig that has to stay assembled. Sockets are provided for a resistor of your own if you would prefer the check to land at a value chosen for your sensor.
What is the board made of and where can it live?
A flame-retardant ABS case, about 2.7 by 1.7 by 0.8 inches, weighing an ounce and a half. It carries no ingress protection rating of its own, so it is designed to live inside something else — a control panel, a machine enclosure, a junction box — and whatever surrounds it provides the protection. A DIN rail clip is available so it can sit alongside contactors, terminals and other control components in a standard cabinet. Full performance is specified from freezing to fifty-five degrees Celsius, with derated operation across a considerably wider range.
What do the accessories do?
Four of them, each solving a specific problem. The DIN rail clip mounts the board in a standard cabinet. The mains adapter supplies DC where there is no control supply available. The trim pot tool is the correct driver for the adjustment potentiometers, which are easy to damage with the wrong screwdriver and awkward to set precisely with anything else. And the replacement terminal block kit gives you a spare block, which is the one worth ordering with the board rather than after something has gone wrong.
Questions From The Field
Can I replace the board without disturbing my field wiring?
Yes, and it is the main reason to choose this version. Isolate the supply, unplug the terminal blocks with the wires still clamped in them, take the board out, fit the replacement, push the blocks back on. Nothing is unlanded, so nothing can go back in the wrong place. Two things make it go even faster: note down your jumper positions and where the potentiometers are set before you remove the old board, and if you keep a spare terminal block wired and labelled on the shelf you can prepare a complete replacement in advance and make the change in a single short stop.
Can I use this to replace an older TMO-1 amplifier?
In most cases yes, and it is a common upgrade. The LCA-RTC covers a wide span of sensitivities and gains, offers both voltage and current outputs on jumpers, and terminates in screw clamps rather than requiring a made-up connector, which usually makes the physical side of a retrofit simpler than the original installation was. What to check before ordering is the same short list every time: your sensor's sensitivity and bridge resistance, the excitation the existing installation uses, what the output currently feeds and in what form, and whether anything downstream is scaled to the old amplifier's output. Send us those and we will confirm the swap and tell you what will need re-scaling.
Which filter setting should I start with?
Start low and open up only if you have to. Begin at the narrowest setting, apply your load or run your cycle, and see whether the output follows the event faithfully. If it does, stop — you have the quietest configuration that does the job. If the output is visibly lagging or rounding off the peaks of what you are measuring, step up one setting and try again. Working upward like that arrives at the right answer in a few minutes and guarantees you are not carrying noise you did not need. Working downward from thirty kilohertz tends to leave people sitting on a setting far wider than their measurement requires.
Something above my filter setting is still getting through.
Expected, and it is a consequence of the filter being two-pole. A two-pole roll-off reduces by twelve decibels for every doubling of frequency past the corner, which attenuates interference rather than abolishing it — something large and close above your setting will still be visible, just smaller. If a specific frequency is the problem, the durable fix is usually at the source rather than in the filter: move the sensor cable away from whatever is generating it, ground the shield at the instrument end only, and check whether the disturbance is actually mechanical, because a real vibration reaching the sensor is a real force and no filter setting makes it untrue.
The terminal block will not grip my cable properly.
Usually a conductor preparation problem rather than a faulty clamp. Strip to the length the block expects rather than by eye — too short and only a strand or two is under the clamp, too long and bare conductor sits outside it where it can touch something. Fine stranded cable, which is what most sensor leads use, benefits from ferrules, which keep the strands together and stop one escaping the clamp and shorting to its neighbour. Tighten firmly and then check by pulling gently on each conductor. If a particular way is genuinely damaged, the replacement terminal block kit exists precisely so the block can be renewed without replacing the board.
How do I tell whether a problem is the sensor or the conditioner?
Divide the chain and test the halves. Shunt calibration is the fastest first move: if the shunt check gives the output it always gave, the conditioner and everything downstream are working and the question is the sensor or the mechanics. If the shunt check is also wrong, the problem is at or before the conditioner. From there, check the excitation voltage is actually present at the sensor terminals, and measure the bridge resistance between the excitation leads and between the signal leads with the sensor disconnected — a reading that has moved away from nominal, or an unexpected connection to the sensor body, indicates a damaged cell or a wet cable rather than anything electronic.
Can this board sit outdoors or in an unheated building?
Not on its own — it has no ingress rating and needs an enclosure appropriate to the environment. Given one, the temperature side is manageable: full specification down to freezing and up to fifty-five degrees Celsius, with derated operation over a much wider band, so an unheated building is generally within reach. The thing to watch in an outdoor or unheated enclosure is not cold but condensation, which forms as a cabinet cools overnight and is a far more common cause of trouble than temperature itself. Tell us the environment and we will suggest an arrangement.
Do I have to re-scale everything downstream if I change the output jumper?
Yes, and it is worth planning rather than discovering. Moving from a ten volt range to a five volt one halves the signal for the same load, and moving from voltage to a current loop changes it entirely, so whatever is receiving the signal has to be told. Do it in a deliberate order: set the jumper, re-check zero and span with a known load or with the shunt calibration, then re-scale the receiving equipment and confirm end to end. The flexibility is genuinely useful — a jumper rather than a new part number — but the change does not stop at the board.