User manual

User Manual
man_905K_1.10.doc Page 37
time - this is to prevent overcrowding of the radio channel. An example could be a system
monitoring environmental alarms. Normally there would be few change messages, but under
abnormal conditions, a lot of change messages could be generated in a short time period. The
paralysis time will allow each module to send the first change message, but subsequent change
messages are disabled during the paralysis time.
There is a separate paralysis time for digital change messages and pulse change messages. There
is no paralysis time for analog inputs.
4.4 Analog Input
There are three parameters
which may be adjusted for
the analog input.
The change sensitivity is
the amount of change since
the last transmission which
will trigger another
transmission for this input.
For example, if the last
transmitted value of the
input was 55.0%, and the
sensitivity is 1.2%, then
another transmission will occur if the measured input value is less than 53.8% or more than
56.2%. If change messages are not required, then a sensitivity of 75% should be selected.
The 905K does not have any filtering on the analog measurement. If the analog signal is noisy,
then a lot of change messages can be generated if the sensitivity value is set too low. The
sensitivity should be set to be greater than the signal noise. For example, if there is a signal
oscillation of 1% on the input, then a sensitivity of less than 1% will result in continuous change
transmissions which could overload the radio channel.
The sample time is the time period for each analog input measurement. Between measurements,
the 905K will operate in "sleep" mode. When the sample time has expired, the 905K will turn on
the analog loop power supply. After a further time, called the warm-up time, the 905K will
make a measurement of the input. The warm-up time allows the transducer to stabilise and
become accurate after the loop supply is turned on.
The sample time may be entered in seconds, between 0 and 32 767 seconds. The warm-up time
may be entered in seconds between 0 and 127 seconds.
If the sample time is less than or equal to the warm-up time, then the analog loop supply will be
always on and measurements of the analog signal will be taken based on the sample time. If the
sample time is zero, then a measurement will be taken every 0.5 sec.
The analog loop supply will be always on, so this situation is not suitable for a battery power
supply.