Instruction manual Operation
21
9.2 Setting the pulse output
The pulse output can be set in two different operating modes:
Volume based mode
After a measured volume of 10 l (preset value), a pulse is sent => 1 pulse/10 l.
The maximum number of pulses that can be sent without storing is calculated using the
two default parameters Vol per pulse =1 and Pulse width = 25 ms, with the formula
1/(0.025x2) giving a value of 20 pulses/s.
If the volume flow in the pipe is so high that more than 20 pulses/s are generated, a pulse
overload error may occur if the number of stored pulses exceed a value of 1,000.
To avoid this, the Vol per pulse value can be adjusted as necessary.
See Section 10 Password-protected menus, Page 23.
Frequency based mode
In frequency-based mode, the pulse output frequency is proportional to the volume flow
within a frequency range of 0 – 200 Hz.
9.3 Current output 4 - 20 mA
The preset output value of 4 - 20 mA is active if the 4 - 20 mA LED is lit.
The preset flow value for the 20 mA output is calculated automatically according to the set
pipe size.
The preset flow value for the 4 mA output is 0. To change this, see Section 10 Password-
protected menus, Page 23.
If the flow value is greater than the value set for the 20 mA output, or there is negative
flow, or a flow signal cannot be detected, then an alarm current of 3.5 mA is generated.
9.4 Modbus
The Modbus RTU interface is configured via the Modbus sub menu in the password controlled
menu.
The data rate can be selected in the range 1200 to 38400 baud.
The address can be set in the range 1 to 126.
Polling Rate 1000ms (1sec). Time out after 5 seconds.
The instrument responds to the “read holding registers” request (CMD 03).
If the flow reading is invalid then the flow value will be zero.
If a temperature sensor goes out of range then the value will go to -11.
Both of these faults will set the relevant status bit.The following registers are available.
On a unit set to Imperial the flow in US Gallons.
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