WI-GTWY-9-xxx Wireless Gateway V1.18
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radio channel. A sensitivity value of 1 in 65535 is a change of 0.0015%. If the host device
writes an analogue value to a WI-GTWY-9-xxx every 100msec, it will change by at least 1 bit
each time. A small sensitivity value will cause a change message to be sent every 100msec. If
there are many analogue values in the same situation, then there would be many change
messages every 100msec. Sensitivity values for analogue I/O should be set to be greater than the
normal process noise of the signal. For example, if a flow signal has a normal process
oscillation of 2.5%, then the sensitivity should be set to 3% (or a value of 2000) to avoid change
transmissions from the process oscillations.
4.6.2
I/O Value Scaling
Firmware version 1.76 and later:
The values in I/O registers can be scaled as the values are transferred to the data bus, or from the
data bus.
The I/O values in the WI-GTWY-9-xxx database registers are stored as 16-bit values (between 0
and FFFF hexidecimal or 0 and 65,535 decimal). Analog inputs at a WI-I/O 9-x I/O module are
scaled hex 4000 (dec 16,384) for 4mA and hex C000 (dec 49152) for 20mA. A 12 mA signal is
half-way in this range at hex 8000 (dec 32,768).
The reason for adding additional scaling between the WI-GTWY-9-xxx database (radio side) and
the data bus is to cater for external host devices which do not handle normal 16-bit values. Two
examples are:
Honeywell Modbus gateways which only handle 12-bits values (0-4,095 decimal), and
Sensor / analyzer devices with “signed 16-bit” values. A signed 16-bit value is a 15-bit value
with an additional bit to signify plus (0) or minus (1).
Scaling of I/O registers can be configured in blocks. Different blocks can have different scaling.
Note that scaling only affects values transferred in or out of the data bus port. It has no affect on
the radio side.
