Tension-Compression Load Cell Selection: Test the Full Reversal Cycle

Tension-compression load cell selection must account for what happens when force changes direction. A fixture can read correctly in a steady pull yet give a different result after pushing because an adapter moves, a joint takes up clearance or the electronics clip negative values. Define the full force cycle and the sign convention before selecting the sensor and its readout.

Tension-compression load cell selection needs a signed force specification

Write the expected tension and compression separately, including fixture weight and intentional preload. State which direction is positive at the instrument and at the receiving PLC. Include reversal frequency, holding time and the force at the point where the machine makes a decision.

The METRAVON MV-LC0190 lists rated loads of 1, 5, 20 and 50 kg. Preserve those catalogue units when identifying the version, but specify the machine's force requirement in a clear, agreed unit. When a test uses newtons, document the conversion used in calibration rather than treating kilograms of mass and newtons of force as the same quantity.

The product's measuring range does not by itself approve the connecting hardware or establish endurance under repeated reversals. Confirm the offered unit's permitted duty, attachment details and calibration scope. If the assembly has only been verified in one direction, that evidence should not be presented as a test of both.

Build a fixture that can reverse without changing the force path

Follow the sensor drawing for the intended attachment features. Align the force application with the sensing axis through the whole travel, not just at the starting position. A moving actuator or a deflecting frame can introduce an off-axis load that varies during the cycle.

For threaded adapters, agree thread engagement, locking and assembly torque with the component documentation. Use the specified method to react tightening torque rather than transmitting it through the sensing element. Do not obtain a seemingly secure fit by bottoming an adapter against an unintended internal surface.

Watch for movement when the force crosses zero. Clearance in a rod end or coupling can allow travel before the opposite face takes load, producing an impact or a discontinuity in the signal. Preload may be part of an engineered solution, but it also consumes mechanical capacity and changes the zero condition. Software taring does not remove that force.

Specify protection for both directions without creating a parallel load path during normal measurement. A compression stop does not necessarily protect the tensile attachments. The restraint and support arrangement must also allow the sensor to be removed without leaving an unsupported load.

Check bipolar measurement from the bridge to the controller

The stated sensitivity tolerances are +/-0.1 mV/V for the 1 kg version and +/-0.2 mV/V for the others. These describe variation in sensitivity, not the uncertainty of the finished force test. The reference excitation range is 4-12 VDC; the listed maximum of 15 VDC is not the normal supply recommendation.

At an illustrative 5 V excitation, the nominal full-scale signal changes are 2.5 mV and 5 mV respectively. Confirm that the conditioner accepts the required positive and negative bridge signals around the installed zero. An input that works for a positive loading test may saturate or suppress the opposite direction.

The standard cable reference is four-wire, 0.2 m. Plan the nearby termination and confirm the permitted extension arrangement. The bare sensor does not supply 4-20 mA or Modbus RTU; those interfaces require a specified conditioner or instrument.

If a current-loop transmitter is used, document how tension, zero force and compression map onto its output range. Do not assume zero force corresponds to 4 mA. Check how the PLC distinguishes a valid negative force from a cable fault or an out-of-range value. The PLC wiring guide covers the separate roles of the bridge input and the controller interface.

Accept the complete reversal cycle, not two isolated readings

Agree a test sequence that includes the normal starting condition, increasing force, unloading, crossing zero and loading in the other direction. Use the final adapters and an appropriate reference. Record the raw signal where available, the indicated force and the PLC value at the same test points.

Compare repeated cycles and the return to zero. A jump at reversal warrants inspection of joint movement and signal processing before changing a scale factor. A steadily different response in each direction needs a controlled investigation of alignment, friction, sensor behaviour and the calibration method.

Retain the filter and sampling settings with the results. A slow static test cannot prove that the same system captures the peak in a fast production cycle. The required operating rate and force-time profile belong in the acceptance plan and the enquiry.

Send the fixture drawing, positive and negative force limits, preload, cycle rate and readout requirements through the METRAVON contact page. Ask the quotation to identify the capacity, attachment arrangement, cable, conditioner and verification required in each direction. This avoids ordering a sensor first and discovering later that the instrument cannot represent half the measurement cycle.

Questions about bidirectional measurement

Q1. Can a sign change in software turn a compression-only cell into a tension sensor?

No. A sign change alters the displayed convention, not the mechanical load path. Tensile service requires an explicitly suitable sensing structure and attachments. Confirm both before considering the electronic sign or calibration.

Q2. Can zero tracking remain active while the actuator reverses?

Only if that operating state is an approved reference condition. Otherwise the controller may erase real residual force or preload while waiting for the signal to settle. Define when zero adjustment is allowed and test it with the actual sequence, including a part that has not fully released.

Q3. Does a factory certificate cover a new set of adapters?

It covers the identified calibration conditions. New adapters can change alignment, clearance and force introduction. Review the certificate scope and verify the modified assembly rather than assuming that the sensor serial number alone makes the previous result applicable.

Summary

Define force and sign in both directions, secure the mechanical interfaces and verify the complete reversal sequence. For MV-LC0190, the capacity-dependent sensitivity and short standard cable are concrete purchasing checks. Acceptance should include the force seen by the controller, not only the sensor's response on a separate bench.