User manual

User Manual
man_905K_1.10.doc Page 13
transmitted for the update time. If an update time of zero is selected, then no update messages
will be sent.
The maximum pulse input is:
 300Hz for contact or NPN inputs (1 msec minimum on-time and off-time), or
 10KHz (30 µsec minimum on-time and off-time) for TTL inputs. Up to 50KHz can be
achieved on PI2 provided the divider is set such that the scaled count rate is less than 10KHz
(see below).
There is no minimum pulse rate. For PI2, there is a configurable scaling divider (integer 1 –
255). This allows the pulse count to be scaled. If a divider of X is configured, then the pulse
count will increase by 1 for each X input pulses. There is a separate divider for each pulse input.
The divider parameter could be used for the following reasons:
 If the pulse count is to be transmitted to a pulse output on a 905U, then the maximum pulse
rate is 100Hz. If the input rate is more than 100Hz, then it can be reduced with the divider.
For example, if the maximum input rate is 300Hz, then the use of a 10 divider will bring the
effective rate down to 30Hz - each output pulse will then represent 10 input pulses.
 The divider can be used to scale the pulse count to engineering units. For example, if the
input pulse rate is 7 pulses per m
3
of gas, then a divider of 7 will result in a pulse count
corresponding to the number of m
3
. Note that the divider must be an integer.
 The divider could be used to slow down the pulse rate. If the input pulse rate is 5KHz, then
the base 16 bit counter will overflow in approx 13 seconds. If the overflow counter is not
used, then this may be too fast to be processed by HMI software. If a divider of 100 is used,
then the counter will take over 20 minutes to overflow.
There is no divider for PI1.
If the pulse count is transmitted to a pulse output on a 905U module, the 905U will compare the
input count to its own output count (the count of output pulses), and will then output pulses until
the two counts are the same. If the pulse counts are transmitted to a 905U-C or 905U-G interface
module, then the 905U-C/G will store the pulse count value in an internal register.
For pulse rates higher than 10 Hz, the “Fast Pulsed Inputs” option should be selected. This
increases power consumption of the module significantly and this needs to be considered if using
a battery power supply.
Overview:
• Pulse inputs are counted as 2 x 16 bit registers.
• Pulse count is transmitted when the count has increased by the sensitivity amount since the
last transmission.
• Update message if the input value has not been transmitted within the update time (10
seconds - 7 days).