Wednesday, 29 January 2020
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A sensor for all suspension media

Donut load sensors were developed to take the increasingly cramped construction space in lifts into account. The sensor is mounted in the rope suspension (dead point) with elastomeric spring buffers or compression springs and is therefore also suitable for very small shaft heads. It makes no difference in this regard whether this involves steel ropes or belts.


The Donut sensor series introduced at interlift 2015 in Augsburg has been supplemented with new sensor types. Apart from the standard Donut sensor, there is now also the Donut Light sensor. Both sensor types are practically identical in terms of installation, handling and also mechanical structure.

Hardened steel in the load-bearing parts

The same applies to their field of application. Both exist in four different models, which are ultimately dependent on the suspension media used and their maximum load. What is decisive in selecting the appropriate model is the internal diameter of the Donut sensor through which the threaded bolt of the suspension media connector is guided and the maximum load per suspension device used.

Great store was set by the load capacity in all load-bearing parts of the sensor. Henning employs hardened steel in the load-bearing parts instead of aluminium. This is for good reasons: on the one hand, the sensor may not become deformed even after an emergency stop and the associated enormous forces, which would require recalibration and on the other, the sensor components rub minimally against each other with each movement of the car. Friction in aluminium results in abraded particles, and as a result in falsification of the measured signal, and possibly even prevention of the deviation compensation.

Henning developed "swashplate”

An equally important aspect in a sensor in which suspension media end connectors are used is the ability to compensate for deviation. Particularly in 2:1 suspended lifts, designed without a machine-room, massive deviation of up to 7° normally occurs in the case of thin ropes at the highest stop. This deviation reoccurs in the threaded rod of the suspension media, but may under no circumstances affect the sensor.

If as a result it were diagonal to the rope plate, the force flow in the sensor would be distorted and could in part result in wide measurement errors. This is why the sensor manufacturer Henning developed the so-called "swashplate”, which is inserted between the sensor and rope plate. This ensures that the sensor is always oriented parallel to the suspension media end connector and as a result generates valid measurement results. The swashplates compensate deviation up to 10°.

Differences between product versions

Since cost intensive electronics and precalibration have been dispensed with in the Donut Light sensor, it must be calibrated after installation with weights. If the lift is a new installation, these are already on the spot and do not involve any additional costs. In this case the Donut Light is a good, because cheaper, version.

The standard Donut sensor can by contrast be used with plug 'n play. As soon as it has been installed in the suspension media end connector, no further work is required – the loads on the individual suspension media and as a result also the entire load can be read immediately. Weights do not need to be brought to the site.

Convenient setting of the rope tension

The standard Donut sensor permits measurement of the absolute individual rope loads. This means it is known what load each of the suspension media is bearing. Apart from the rope adjustment, this also means that the total absolute weight of the car is known. As a result, the car tare weight can be determined, which can be very helpful in modernisations. The Donut Light sensor is unable to do this.

If the standard Donut sensor is used and the absolute individual loads can as a result be used, free software from Henning permits convenient setting of the rope tension. The software guides the fitter step-by-step through the rope adjustment.

Each rope of the set is adjusted to an optimal tension calculated by the software. This means that each rope is only touched by the fitter once and consequently adjusting a complete rope set, even if it consists of 12 ropes, only takes a few minutes.

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