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Digital load cell.

Product News Monday, April 11, 2011: Multi-Weigh Technologies

Multiweigh has imported the first Vishay Digital Loadcell to be used in a high accuracy, checkweighing application on a fast moving conveyor, the  Vishay - 240D Load Cell.

Product Description

Model 240D is specifically designed for high speed/dynamic weighing. Fluid damping vastly improves the response time and fatigue life over undamped load cells. On board electronics make it easily configurable and simple to employ in approved weighing applications. A wealth of application experience has gone into this load cell to allow weighing system designers to expedite development of their own designs - a great proportion of the functionality required to create a fully featured weighing system is already implemented in the 240D.

Communication is straight forward using an ASCII or MODBUS command structure where high update speeds are possible, making the 240D particularly suitable for check weighing. RS232 interface is available for single load cell applications and simple load cell setup.In multi-head weighing machines, up to 128 units can be networked together over an RS485 link. 4 digital inputs allow the synchronization of the weighing with external triggers and remote operations (zero, tare). 4 digital outputs enable control functions like coarse and fine rate filling, and relieve the real-time load of the system controller.

Factory calibration ensures that each unit will be virtually identical in performance. Graphic User Interface (GUI) PC application enables easy monitoring, setup and calibration of all load cells connected on the RS485 network. Load cell parameters can be retrieved and store for backup, and downloaded into the load cell for easy recovery from failures or changing operating modes.

Application

• High speed/dynamic weighing

Basic Features

• Fully calibrated and filtered digital output
• High update rate, up to 1200 updates per second
• Checkweigher function - reading acquired over period set by
• remote sensor trigger
• 4 opto-isolated digital inputs
• 4 opto-isolated digital outputs
• Advanced configurable digital filtering
• Safeguard access to calibration data for approved applications
• Reading on request or continuous output
• Visual indication of operating mode and errors
• Extensive diagnostics Fluid damped and overload protected
• Graphic User Interface (GUI) PC application enables easy setup, calibration and monitoring

Diagnostics

A significant advantage of the digital load cell is in terms of cost of ownership. The analogue load cell, especially in multi-cell applications can be awkward to set up and fault find. In a production line environment, the real cost of determining and resolving equipment problems is high. Reliable and meaningful feedback about load cell operation and fault conditions are essential for fast recovery and this is where the 240D pays for itself.

The 240D has a number of key features in terms of diagnostics foe cell operation:

1. External indication of errors - a bi-color led is used to show status and fault conditions. Even in the worst case, if communication with the load cell is not possible, the 240D can still give an indication of its health and set up.
2. Validity of readings - with each reading, status characters are transmitted (good/bad/warning). Fatal errors cause readings to cease and error codes are transmitted.
3. Integrity of calibration - at power up the cell(s) self check to assure:
   
   • Calibration
   • Consistency between units used in combination
   • The network has been changed- units added/removed