A sensor has failed, the manufacturer no longer supplies the type, or the lead time does not fit the planned shutdown. In all three cases the question is the same: which cell fits in place of the old one?
The good news is that a strain gauge load cell is not a closed system. It is a spring element with a full bridge, and its behaviour can be described completely by a handful of values. If those values and the mechanics match, the replacement is electrically and mechanically equivalent – regardless of who built the old cell.
What to read off the old sensor
Most of it is on the nameplate or in the calibration certificate. What is missing can be measured.
- Rated capacity in kg, t, N or kN – and whether it is tension, compression or both.
- Rated output in mV/V. Typical values are 1, 2 or 3 mV/V. This is what decides whether the existing electronics keep working without rescaling.
- Bridge resistance in ohms, measured across the signal leads. 350 Ω is the most common value; 700 Ω and 1000 Ω also exist.
- Excitation voltage the cell is designed for – and what the existing electronics actually supply.
- Connection: 4-wire or 6-wire, cable length, colour code or connector pinout. The colour code is manufacturer-specific and has to be translated, not copied.
- Mechanics: thread, hole pattern, mounting height, point of load application. This is where it is decided whether the cell is swapped or adapted.
- Protection rating, material, temperature range – and whether an approval is attached: ATEX, trade approval, SIL or performance level.
A photo of the nameplate and one of the installation are usually enough to start.
Three routes to a replacement
An equivalent standard type
If rated capacity, rated output, bridge resistance and mechanics match, the cell is replaced from the range. octogon supplies load cells and force transducers from 1 N to 10 MN in the common designs – shear beam and bending beam, S-type, button, column, ring, single point, load pins.
Adaptation to the existing mechanics
If the electrical side matches but the hole pattern or the height does not, the cell is adapted. Adapter plates, changed threads or an altered mounting height are routine through our own CNC machining – usually faster and cheaper than rebuilding the plant around a new cell.
Rebuild from a sample or a drawing
If the type no longer exists and no standard design can be transferred, the sensor is rebuilt: design the spring element, machine it, apply the strain gauges, seal it and calibrate it. An old cell as a sample is often enough; a drawing is better.
When the electronics are affected too
If the old amplifier failed as well, or the installation is to be modernised at the same time, the evaluation side belongs in the plan: weighing transmitters for the PLC, indicators for operation on site, IO-Link for a digital connection. A frequent case in modernisation: the old cell stays and only the amplifier is exchanged for one with a digital output – installation and mechanics remain untouched.
Asking for a replacement
Send to office@octogon.org:
- a photo of the nameplate and of the installation
- rated capacity, rated output in mV/V and bridge resistance, as far as known
- what the existing electronics are
- by when it is needed
Or call +43 676 362 8453. Delivery takes 3 to 5 working days within Austria and 5 to 7 working days abroad, unless the offer states otherwise.