August 1999
Inclinometers
Our inclinometers can be used for controlling devices which must be horizontal during operation.
Examples includes:
working platforms such as lifts etc.
agricultural machinery
earth moving equipment
cranes
The devices are constructed to meet the high security specifications applying to this type of equipment. (EN280)
Our inclinometers contains no mercury
The principle of operation is a electrolytic fluid which is being monitored by electrodes. The digital signals from the sensor electrodes are being processed in the on-board computer. Active logical filters removes the influences of vibrations .
The software constantly monitors and evaluate the validity of the signals and the state of the hardware. In the case of an error, the safety current outputs are switched off.
In the event of a hardware failure, the watch-dog timer switches the safety current outputs off.
Products :
1 Inclinometer with digital outputs only
2 Inclinometer with analog and digital outputs
The inclinometer contains 3 separate functions :
A directional switch which activates when the unit tilts by more than 0.5 degrees. from horizontal and the enable signal is high (24 volt).
A directional switch which activates when the unit tilts by more than app.3 degrees. from horizontal regardless of the enable signal.
A directional switch safety switch which activates when the unit tilts by more than 10 degrees. from horizontal regardless of the enable signals.
The normal mode of operation is by function 1. If however, there is a leak in the hydraulic valve so the platform slowly sags, the unit will switch to function 2. when the unit has tilted app. 3 degrees.
In this situation the unit will start the motor and try to bring the platform up to level .
If this attempt fails and the platform tilts further till app. 10 degrees, the unit switches to function 3 and cuts off the safety current thus halting the lift.
The ELv is constructed with a AVR microprocessor from Atmel. This processor controls and monitors the electrolytic sensor, 2 on/off inputs, 4 transistor outputs and an amplifier and a A/D
converter circuit.
The processor controls the following tasks:
Generate control signals to the electrolytic sensor.
Reading the A/D converter.
Monitoring the inputs.
Calculate the angle of tilt and apply signals to the outputs according the inputs,
Monitoring and controlling the outputs constantly checking that everything operates normally.
The electrolytic sensor (ETS) contains a fluid which is in contact with 3 electrodes. When the sensor tilts the resistance between the electrodes changes. This change is registered by the AD/converter and the processor.
The type of sensor which is used in this device is equipped with 5 electrodes. It is therefor possible for the computer to register the tilt in two planes perpendicular on each other.
The two inputs supply information to the processor if the boom is raised or lowered.
The two outputs are intended to be connected to the motor control circuit.
The signals can alternatively be fed to the Power module which can control the speed of the motor ( ELvP)
Specifications of standards and how the device comply.
Because the ELv is intended for lifts it has to comply with (prEN280).
Under prEN280 there are especially two sections which are of interest.. Section 5.7 dealing with electrical equipment,
and section 5.11 dealing with security equipment.
electrical equipment.
The regulations require that all electrical equipment on a lift shall fulfil ICE norm NE 60204-1 : 1992 electronics in machinery. In NE 60204-1 there are references to general specifications for EMC requirements for industrial equipment, (ICE801 part 1-4)
security equipment.
According to prEN280 this levelling system is a safety device. In prEN280 it is required that the sensing device shall be doubled and constantly monitored, or that the signals shall be verified by information from another sensor. And components shall be designed for twice as many operations as the lift itself.
The above described requirements are interpreted in this way: It is the sensor (the glass tube with the electrodes ) which has to comply with the above specifications.
The rest of the electronics has to comply with the requirements that it shall be capable of lasting twice as many operations as the lift.
Redundancy and constant monitoring.
The sensor is of a special type capable of measuring the tilt angle in two planes. Because the sensor is mounted in such a way that it provides signals on both outputs even if only one axis are measured, one can regard the device as redundant.
In addition any failure of the sensor ( the glass being broken ) will cause missing or abnormal signals which are instantly detected by the processor and the alarm is set.
The signal are verified by another unit.
Because the ELv receives information from the crane if the boom is lowered or raised, the processor can compare these signals with the signals from the tilt sensor.
If the boom is moved it shall be recognised by the sensor as a change in the angle. If this is not the case the processor will after app. 10 sec conclude that there is a failure on the lift or on the sensor and the alarm will be set.
Electrical equipment.
Because there are no mechanical moving parts in the ELv and because the components are only light loaded with respect to there specifications, the ELv has a theoretical lifetime hundred times the lifetime of the lift..
Schematics.
|
Connections. |
|
|
Pin No. |
Function |
|
1 |
Control signal boom up (input) |
|
2 |
Control signal boom down (input) |
|
3 |
Levelling signal "down" (output) |
|
4 |
Short1 |
|
5 |
Short 2 |
|
6 |
Short 3 |
|
7 |
+24 Volt supply |
|
8 |
Ground |
|
9 |
10° alarm "up" (safety-output) |
|
10 |
10° alarm "down" (safety-output) |
|
11 |
short 3 |
|
12 |
short 2 |
|
13 |
short 1 |
|
14 |
Levelling signal "up" (output) |
These inputs are active by applying +24 volt.
The 4 outputs can source a current of Max 1 Ampere.
The outputs are protected against short circuit and overload.
The outputs are capable of driving inductive loads
The device is projected against reversal of supply and against over voltage to 38 volts.
However, if the voltage is reversed all outputs are active without protection
There are 3 shorts for aid of external wiring. Max current is 4 A.
Models.
ELvP , Electrolytic Proportional Sensor
PWM Pulse-With-Modulated outputs at pin 14 and pin 3.
This device is intended to operate with the Power-module. With this configuration and an adequate design of the hydraulic and mechanical systems it is possible to maintain the platform level within +- 1 degree,- also during movements of the boom of the crane !
ElvD , Electrolytic Digital Sensor
Digital outputs at pin 14 and pin 3.
This device is designed to control the relays of the motor. The platform will start and stop the movements abruptly.
Attainable accuracy : +- 1 - 3 degrees.
This device is manufactured in various sizes from 20 to 300 Ampere.
The Power module is designed to work with the ELvP and is capable of regulating the speed of the motor continuously from 0 to Max rpm dependable on the demand for movement of the platform.
The PWMd is protected against overload but not short circuit.
|
Connections. |
|
|
Pin N0. |
Function |
|
1 |
Control signal up (input) |
|
2 |
Control signal down (input) |
|
3 |
Gnd |
|
4 |
Solenoid A |
|
5 |
Solenoid B |
|
6 |
Gnd |
|
7 |
NC |
|
8 |
Gnd |
|
9 |
+24 Volt Supply |
Specifications:
The tilt switch has built-in protection against :
Reverse polarity
Over voltage 50% for infinity duration
Transients on the supply voltage
Max. ratings:
Supply voltage: 12 - 24 volt
Supply current: 100 mA ( typical )
Temperature: -20 to 50 deg.Celcius
Acceleration: equivalent to a drop from a height of
3 m on a concrete floor.
Plastic box , IP56 for fitting is included: 120 mm x 55 mm x 85mm
It is possible to adjust the switch 10 degrees after the box has been fitted.
The electrical and mechanical design has been developed to meet the requirements for mobile equipment exposed to harsh environment.
