ELZET80 - Industrial Electronics
Motor Current Transducer and Monitor
- Overload protection for screw conveyors, feeders, compactors, balers, shredders...
- Programmable current-proportional pulses to PLC up to 60 kHz
- Real time digital outputs for warning and shutoff
- Set levels fixed (EEPROM) or from trim-pots
- Isolated (IR) serial line for config and charting
- Load range 3 to 37 kW (5..70A), more with external transformer
- 22.5mm rail mount unit, 24VDC i/o
- Conditional history save to internal EEPROM
- Needs just one motor line to be fed through
- 24V input as log trigger or special purpose
- Modern ARM Cortex M3 32-Bit microcontroller
- Comprehensive PC configuration/charting
- Option: cosφ and voltage measurements
- Option: Large flash logging memory (1M Byte)
Current-to-frequency conversion and level monitoring of asynchronous motors for overload ("container full" for screw conveyors @ 1.5 of nominal current) and block (obstruction @ 8 fold nominal current). Digital outputs allow immediate action to prevent lockout or blowing the fuse. History storage of problem courses for analysis of faults and wear.
Three-phase asynchronous motors driving compactors, balers and similar machinery have to be monitored for excessive currents in order to detect overload situations or even blocking. MOTPROTECT provides a current-proportional frequency that may conveniently be counted by any standard PLC. The 14-bit analog input gets continually converted (every 20ms) to the output frequency. The conversion factor (how many pulses per Ampére) can be set in software to match the input capabilities of your PLC. Analysing the current can not only help to decide when to shut off, but also to detect long-time wear or residue. Continuously calculating a temperature model of the motor might allow using a smaller motor while introducing off-times when needed.
Optimising the PLC for high resolution calculations requires long acquisition times that contrast with the need to shut off within less than 100ms in a real block situation. Here MOTPROTECT uses its internal data probed every 20ms to decide about a critical situation and raises a 24V output (optoisolator) to shut off immediately - either through the PLC or directly actuating the motor relay.
Logging
Making use of the powerful little processor in MOTPROTECT, the unit comes with comprehensive configuration software that allows to set the alarm levels fixed (such that the pots on the device have no effect) or adjustable with endpoints and tick steps tunable to field requirements. PC connection to the unit is well isolated with a USB infrared transceiver at 115.2 kBit/s (USB-IRDA) that can be held at distance or hung to the device.
A chart is shown in the graph tab of the PC software while connected, it can be saved as CSV for later Excel® or data base integration. A separate plot utility allows you to look at stored data with adjustable window and scale sizes.
The big advantage over passive devices is the option to store histories of current courses to the device internal EEPROM. Log storage is conditional and can be triggered by the current passing shutoff or warning levels, a manually defined level, or an external input. Times before and after trigger can be adjusted as well as the acquisition timing. Standard memory is 3000 points, an optional data flash stores 500,000 points.
An extended version of MOTPROTECT can capture and store cosφ and voltage.
