Specifications

Chapter 13: Indicators and Applications
Indicators
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Indicators and Applications
Indicators
The basic job of a scale indicator is to receive the signal transmitted by the load cells
and display it as a weight reading. For process weighing applications, indicators must
provide fast, repeatable weight readings that remain stable at relatively high resolutions.
But in many cases, the key factor in selecting an indicator is its ability to communicate
with the process control equipment used for a specific application.
Communications
What type of communications capabilities an indicator needs depends on how you plan
to use the weight data provided by the scale. For a very simple process, an indicator
might use setpoints to tell an operator when to manually fill or empty a tank. For an
automated process, the setpoints could actually control valves or feeders. For more
complex systems, an indicator might need to interact with a programmable logic
controller (PLC) that runs an entire processing operation.
An indicator’s ability to interact with other equipment is determined by its communication
inputs and outputs. The types of inputs and outputs are described below:
Discrete Input/Output
Discrete inputs are connections used to send commands from an indicator to a scale.
Typical commands are Clear, Tare, Print, Zero, switch weight units, switch scales, and
disable weight display.
Discrete outputs are connections used to relay on/off information from the scale. They do
not transmit actual weight values. Discrete outputs can be used for setpoints or scale
status information such as scale in motion, zero, under zero, over capacity, and
net/gross weighing mode. Because they are a direct connection from the scale to the
indicator, these outputs operate very quickly.
BCD Output
Binary Coded Decimal (BCD) outputs transmit weight values in a binary code format
that can be used by a PLC or other device. For each digit of a weight value, the indicator
sends a coded 8,4,2, and 1 output. Cabling normally limits the location of the indicator
to within 10 to 15 feet of a PLC.
Analog Output
Analog output is the variable signal of DC voltage that represents a weight value, which
can be used by a PLC located up to 50 feet from the indicator. The weight data is
converted several times during its transmission from load cells to PLC, with the signal
losing a percentage of its accuracy for each conversion.
Serial Communication Output
Serial communication ports are used to send weight data from the scale to a remote
display, fill valves, computer, PLC, printer, or other equipment. These outputs can
transmit information about scale status, scale capacity, increment size, setpoint status,
weight unit, and net/gross weighing mode. Serial outputs can transmit more information