A DIN rail load cell transmitter is a compact module that clips onto standard rail inside an enclosure, excites a bridge sensor, and converts what comes back into something a control system can use — a current loop, a voltage, a Modbus register, a relay action. It has no display, because the answer is going somewhere else.
The SST-LV differs from its sibling in exactly one respect: it runs on low voltage. Ten to forty-eight volts DC, or low voltage AC. Everything else — the converter, the accuracy, the isolation, the outputs — is the same instrument.
That one difference is not a convenience. It changes what the installation can be.
First, there is no line voltage involved. An enclosure containing only this transmitter never has mains inside it. That changes the box you specify, the wiring practice around it, who is permitted to open it and what happens when it is inspected. A small box carrying twenty-four volts is a fundamentally different object from one carrying line voltage, and on a machine where somebody will eventually need to get into it, that distinction is worth having.
Second, and much more importantly, it can go out to the sensor. This is the argument worth understanding, because it inverts how most people wire a load cell installation.
A strain gauge bridge produces a signal of a few thousandths of a volt. That signal is the fragile part of the entire measuring chain — it loses amplitude to cable resistance, it picks up interference from anything sharing its route, and it is the one part of the system that noise can meaningfully corrupt. The usual arrangement runs that fragile signal all the way from the machine back to a cabinet, which is precisely the wrong way round.
The better arrangement is to convert at the sensor and send something robust the long way. Put the transmitter in a small rail enclosure near the load cell, let the millivolts travel a couple of feet instead of two hundred, and send a current loop or a Modbus message the rest of the distance — neither of which cares about cable resistance, and both of which shrug off interference that would ruin a low level signal.
What has always stopped people doing that is power. Getting line voltage out to a box on a machine is a job: conduit, a disconnect, someone qualified, an inspection. Getting twenty-four volts out there is two wires from a supply that already exists in the panel. The low voltage input is what makes the good arrangement the easy one, and that is why this version exists rather than being a variation for the sake of it.
Third, it will run on things that are not a wall socket. A ten to forty-eight volt DC input spans all three standard DC control voltages — twelve, twenty-four and forty-eight — which means batteries, vehicle systems, mobile equipment, solar installations, and anything behind a UPS that has to keep measuring when the line supply does not. None of that is available from a mains-powered instrument.
And it takes low voltage AC as well as DC, which matters more than it sounds. A great many machines have a control transformer producing twenty-four volts AC and no DC supply anywhere. This module connects to it directly, with no rectifier, no separate power supply and nothing extra in the panel.
The sensor is excited, the returning signal is converted and scaled, and the result leaves by whichever routes you configured. What is worth knowing is how much of that is settled by jumpers, how much by software, and how much the sensor can decide for itself.
Three things are set by internal jumpers: the signal range, the communication type and the excitation level. Those are the decisions that involve the hardware, and having them physical rather than in software has a practical advantage — the configuration is visible to whoever opens the unit, it survives a firmware or PC problem, and it cannot be changed remotely by accident. It also means those three should be settled before installation rather than after, because getting to them means taking the module off the rail.
Everything else is configured from a PC. A serial connection and the instrument setup software give you a graphical interface for scaling, filtering, relay thresholds, output ranges and protocol selection. That is markedly quicker than any front panel could be, and it has a benefit worth planning around: a configuration can be prepared once and applied to a whole batch of transmitters identically, which is what you want when a machine has six of them.
And with a TEDS sensor, part of it happens by itself. Connect a transducer carrying an IEEE 1451.4 memory and the transmitter detects it and takes what it needs from the sensor rather than from you. On a module with no display that is worth more than usual, because a wrong scale factor here produces a confident and completely incorrect signal with no number anywhere for a person to notice looks wrong.
The excitation output is isolated from the instrument's own ground. That is a detail people skip and it matters in exactly the installation this product is built for. If the transmitter is powered from a machine's twenty-four volt bus, and the sensor is bolted to that same machine, the sensor's mounting and the supply's ground can easily be connected through the structure. An isolated excitation output means the measuring circuit is not tied to the power circuit, so whatever the machine's ground is doing does not become part of your signal.
Every other port is isolated too — power, signal, analog output, relays and communications — each rated to 250 volts rms and tested at 4.2 kilovolts. On a module powered from the machine rather than from a clean panel supply, that separation earns its keep every day.
The converter is deliberately tied to the power line and deliberately unhurried. It converts sixty times a second on sixty hertz systems and fifty on fifty hertz, so each conversion spans a whole line cycle and mains interference largely cancels itself before anything else happens. Selectable digital time constants then run from eighty milliseconds all the way out to more than nine seconds, which sounds extreme until you remember what a transmitter is for: a control loop needs a number that sits still far more than it needs a fast one.
What comes out is a complete set of interfaces from one module. A sixteen-bit isolated analog output, selectable between current and voltage and accurate to a fiftieth of a percent of full span. A serial port that can be RS232 or either flavor of RS485, talking Modbus in two forms or straight ASCII. Two solid state relays for local limits. You are not choosing between the analog path, the digital path and the alarm path — you get all three.
The main decision here is where the module goes, and the supply question usually answers it. Our applications engineers are glad to look at a panel layout and a cable schedule together rather than one at a time.
Decide first whether the transmitter goes near the sensor or back in the cabinet. If the run from load cell to cabinet is long, passes near motors or drives, or shares a duct with power wiring, put the module out at the machine and send a robust signal home. If the sensor is already a few feet from the panel, keep it simple and mount it on the rail with everything else. The rule of thumb is straightforward: shorten the millivolt run wherever it is practical to do so, and let the current loop or the serial link do the traveling.
Then work out what supply is actually available where you want the module to sit. A twenty-four volt DC control bus is the usual answer and is ideal. A twenty-four volt AC control transformer works directly. A battery, vehicle or solar system anywhere between ten and forty-eight volts DC is fine. If none of those reach the location, either take a pair of wires out to it or use the line-powered version instead — and that choice is genuinely worth five minutes at the design stage, because it is awkward to reverse afterward.
Give the transmitter a clean supply if you can. Sharing a twenty-four volt rail with solenoids, contactor coils and valve manifolds is common and usually fine, but those loads put spikes on the bus every time they switch. The module is isolated, which handles the worst of it, but a supply that is already well behaved gives the measurement an easier life. Where a machine's control bus is genuinely busy, a small dedicated supply or a filter is cheap insurance.
Settle the three jumper choices before anything is installed. Signal range, communication type and excitation level all live inside the unit, so decide them at the bench. Work out your full scale signal from sensitivity multiplied by excitation, pick the range that fits it most tightly, and choose the serial format from what the plant network needs rather than from what is easiest to test with.
Plan the RS485 line as a network, not as a cable. If several transmitters are going to share a link, think about the wiring topology, the addressing and the termination at the outset. Retrofitting a proper multidrop arrangement onto a set of point-to-point cables is a much bigger job than laying it out correctly once.
Allow for the enclosure and the temperature. Nothing about the module itself keeps dust or water out — that job belongs entirely to the box you put it in. It will work up to seventy degrees Celsius, which is generous, but a small sealed box out on a machine in the sun can exceed what you expect, and so can the inside of a crowded cabinet. Measure rather than estimate if there is any doubt.
Specify TEDS on the sensors where units get swapped. The Cal-Teds plug and play option lets the sensor carry its own identity and calibration, so a replacement transducer configures the transmitter rather than requiring somebody to reconfigure it. On an instrument with no display, that removes the one error nobody can see.
Tell us the sensor, the distance from sensor to panel, what supply exists at each end, what has to receive the signal and how fast the measurement changes, and we will confirm which version and which configuration you want before you order.
SST-LV Load Cell Transmitter Applications.
The Transducer Techniques SST-LV is a plug and play smart TEDS IEEE 1451.4 compliant transmitter powered from low voltage DC or AC, mounting on standard 35 mm DIN rail and providing isolated analog, serial and relay outputs from a single module.
- Sensor-Local Conversion: Mounted in a small enclosure at the machine, the module shortens the millivolt cable run and sends a robust signal the remaining distance.
- 24 Volt Control Systems: Powered directly from the DC control bus a machine already has, with no line voltage required at the module.
- Control Transformer Installations: Accepts low voltage AC, so a machine with a 24 Vac control transformer and no DC supply needs nothing extra.
- Battery and UPS Backed Measurement: A 10 to 48 Vdc input allows measurement to continue through a line supply interruption.
- Mobile and Vehicle Equipment: Suits 12, 24 and 48 volt DC systems on trucks, trailers, cranes and mobile plant.
- Remote and Off-Grid Sites: Runs from solar or battery power where bringing line voltage to the measurement point is impractical.
- PLC and SCADA Integration: Isolated 4–20 mA output and Modbus over RS232 or RS485 deliver the measurement to a controller or supervisory system.
- Multi-Channel Installations: One transmitter per sensor on a shared RS485 line gives independent channels polled by a single master.
- Low Voltage Enclosures: Junction boxes containing only low voltage equipment, simplifying wiring practice and access.
- OEM Machine Building: A compact CE approved rail module that runs from the control voltage a machine already distributes.
The SST-LV works with our full range of load cells, torque sensors and pressure transducers, and is supported by power adapter, serial cable, TEDS reader-editor and data logging software accessories.
Frequently Asked Questions
What supply does the SST-LV need?
Low voltage, either DC or AC. The DC input spans ten to forty-eight volts, which covers twelve, twenty-four and forty-eight volt systems, and it will also run from low voltage AC of the kind a machine control transformer produces. That is the single difference between this and the line-powered version in our range — converter, accuracy, isolation, outputs and physical size are otherwise identical. A plug-in adapter is available where no suitable supply exists and the module simply needs powering from a socket.
Why would I choose the low voltage version?
Because of where it lets you put the module. Most machines already distribute twenty-four volts everywhere, so a pair of wires reaches any point on the equipment, whereas taking line voltage to a box on a machine involves conduit, a disconnect, qualified labor and an inspection. That freedom matters because the best place for a transmitter is usually next to the sensor rather than back in the cabinet. There are two other reasons: an enclosure with no line voltage in it is easier to specify and safer to open, and a low voltage input allows battery, vehicle, solar and UPS-backed operation that a mains instrument cannot offer.
Can I power it from the same supply as my PLC?
Usually yes, and it is the normal arrangement. The module's power input is isolated from its measuring circuit, so sharing a supply does not tie the sensor's circuit to the controller's. The caution is about supply quality rather than about grounding: a control bus also feeding solenoids, contactor coils and valve manifolds carries a spike every time one of those switches. That is generally tolerable, but if a machine's twenty-four volt rail is heavily loaded with switching devices, a small dedicated supply for instrumentation is inexpensive and removes a whole category of intermittent problem.
Does it really accept AC as well as DC?
Yes, low voltage AC as well as DC, which is more useful than it first appears. A great many machines have a control transformer producing twenty-four volts AC and no DC supply anywhere in the panel. Rather than adding a power supply just to run an instrument, the module connects to the transformer directly. If you are working from a design that assumed DC and the panel turns out to have only AC, that is not the obstacle it would normally be — send us the transformer details and we will confirm the connection.
Can I put the transmitter out at the machine instead of in the main cabinet?
That is the arrangement this version is built for, and it is usually the better engineering. A load cell's output is a few thousandths of a volt and it is the part of the chain most easily degraded by cable resistance and interference. Convert it at the sensor and the fragile signal travels a couple of feet instead of a couple of hundred, while a current loop or a serial message covers the distance instead — neither of which is troubled by either problem. You will need a small rail enclosure appropriate to the environment, and a pair of wires for the supply, which is exactly what the low voltage input makes easy.
How is the transmitter configured?
Partly by internal jumpers and partly from a PC. Signal range, communication type and excitation level are jumper settings inside the unit, so those should be decided at the bench before installation. Everything else — scaling, filtering, output range, relay thresholds, protocol — is set through a serial connection using the instrument setup software, which gives a graphical interface and is considerably quicker than any front panel would be. It also lets one configuration be applied identically to a whole batch of modules, which is what you want when a machine has several. With a TEDS sensor connected, the transmitter takes what it needs from the sensor itself.
How many transmitters can share one RS485 line?
Several, and that is the usual arrangement for a multi-sensor machine — each transmitter has its own address and a single master polls them all over one pair of wires, which is far tidier than running an analog output from every module. The practical limits come from the network rather than from the transmitter: the number of devices a line will support, the cable length, the baud rate and correct termination all interact. Plan the topology, the addressing and the termination before installing rather than afterward, and tell us how many channels and what distance you are dealing with and we will help you lay it out.
What excitation does the module supply, and is it isolated?
Ten volts as supplied, with five and twenty-four volt settings also available by jumper, and the output is isolated from the instrument's own ground by fifty volts. That isolation matters particularly here, because a module powered from a machine's control bus and reading a sensor bolted to the same machine could otherwise find the sensor's mounting and the supply ground connected through the structure. Isolating the excitation keeps the measuring circuit separate from the power circuit. Do check the available current against your bridge before selecting the highest setting, since the twenty-four volt option supplies the least current of the three.
How accurate is the SST-LV?
Input accuracy is 0.01 percent of full span plus two counts at twenty-five degrees Celsius, with the analog output adding a further 0.02 percent of full span. Zero drifts by 0.2 microvolts and span by 0.0015 percent of reading per degree Celsius. Conversion is sixteen bit at sixty times a second on sixty hertz systems. Those figures are considerably better than any load cell you can connect, which is the correct relationship for something in the middle of a chain — when a measurement disappoints, the sensor and the mechanical arrangement are where to look, not the transmitter.
What accessories are available, and what is each one for?
A plug-in DC adapter, for powering the module where no suitable supply exists at the location. A serial cable and a serial-to-USB adapter cable, for connecting a PC to configure it — you will need one of these unless every sensor you use carries TEDS. An adapter connector for wiring a sensor to the unit. And two software packages: one that reads and writes what is stored in a sensor's TEDS memory, which is what a calibration laboratory needs, and one for logging data to a PC. The setup software itself is a free download.
Questions From The Field
My reading moves whenever the machine's solenoids fire.
Look at the supply before the sensor. A twenty-four volt control bus shared with solenoids, valve manifolds and contactor coils carries a voltage spike each time one of them switches, and while the module's isolation handles most of that, a heavily loaded rail is a rough environment. Try a separate supply for the instrumentation, even temporarily, and see whether the disturbance follows. If it does, a dedicated supply or a filter on the existing one is the fix. If the reading still moves on a clean supply, the coupling is happening at the sensor cable instead — check its routing away from the solenoid wiring and confirm the shield is grounded at one end only.
I want to run this from a battery. How far down can it go?
The DC input works down to ten volts, so a twelve volt battery gives you useful margin as it discharges and a twenty-four volt system a great deal more. Two things to remember on a battery installation: the module also has to power your sensor's excitation, so the total draw is larger than the transmitter alone, and a battery that sags under a separate heavy load can dip the supply momentarily even though its resting voltage looks healthy. Tell us the battery, what else is on it and which sensor you are using, and we will work out whether a stabilized supply is worth adding.
My sensor cable is long and the signal is noisy.
Then move the conversion rather than fighting the cable. Every foot of low level signal wire is an opportunity to lose amplitude to resistance and to pick up whatever is nearby, and past a certain distance no amount of shielding and routing fully solves it. Put the transmitter in a small enclosure at the machine, keep the sensor lead as short as the mechanics allow, and let a current loop or a Modbus link carry the measurement back — both are far more tolerant of distance and interference than millivolts will ever be. Being able to power the module from a couple of wires is precisely what makes that practical.
My panel has 24 volts AC from a control transformer, not DC.
That is fine and needs nothing extra. The module accepts low voltage AC as well as DC, so it connects to a control transformer directly without a rectifier or an added power supply. Confirm the transformer has capacity for the module and its excitation load alongside whatever else it already feeds, since control transformers are often specified tightly for the contactors they were bought for. If you are unsure of the numbers, send us the transformer rating and the sensor and we will check it.
Can one supply run both the transmitter and the sensor?
It already does, and that is the point of the arrangement. The transmitter generates the sensor's excitation itself from whatever supply you give it, so you provide one low voltage feed and the module looks after the sensor. There is no separate excitation supply to specify and no second power run to the machine. What is worth checking is the total draw on the supply if several transmitters share it, since each one is powering a bridge as well as itself — four modules with four load cells is a different load from four modules alone.
Which do I need, the low voltage version or the line powered one?
Answer one question: what supply exists where the module will sit. If there is a twenty-four volt DC bus or a low voltage AC control transformer at that location, or if the module needs to run from a battery or through a power interruption, take the low voltage version. If the module is going in a main cabinet that already has line voltage and no low voltage rail, the line powered version saves you adding a supply. Everything else about the two is identical, so the decision is purely about the panel — and it is much easier settled before ordering than after delivery.
My Modbus master cannot see the transmitter.
Work through the settings in order, because it is nearly always a mismatch rather than a fault. Confirm the serial format jumper matches what you are actually wired for, since RS232 and the two RS485 modes are a hardware selection inside the unit rather than a software one. Then check that address, baud rate, parity and protocol variant agree at both ends — Modbus RTU and Modbus ASCII are not interchangeable and a master set for one will see nothing from a device set for the other. On RS485, check the polarity of the pair and that the line is terminated correctly. If all of that is confirmed and it is still silent, contact us with the configuration.
Does the supply need a fuse or any protection?
Treat it as you would any other instrument on the control bus and follow your own panel standards, which will generally call for protection appropriate to the wiring rather than to the device. The more useful precaution in a machine installation is what happens on the supply rather than to it — a rail shared with inductive loads benefits from suppression at those loads, which protects everything on the bus rather than just this module. If you are designing the panel and want the specifics for your arrangement, ask us with the supply details and the number of modules and we will go through it.