Additional Information For The Pulse Output - ABB MAG-SM Instruction Bulletin

Electromagnetic Flowmeter Converter
9.3

Additional Information for the Pulse Output

The scaled pulse output can be ordered as a 2-channel pulse output, separate for forward and reverse in an active (24 V DC) or
passive (optocoupler) design. When configuring the parameter the following settings must be entered.
Parameter Entry
Pulse factor
1.0000 / m3
Pulse width
230
Totalizer units
m3
50
Pulse Factor
The pulse factor is the number of output pulses for one measured flowrate unit. When the pulse factor is
changed, the totalizer value in the selected units remains unchanged. The pulse factor can be selected
in the range from 0.001 to 1000 pulses/unit.
The selected pulse factor is checked by the converter as a function of the flow range, the pulse width,
the volume (e.g. ml, l, m3 ) or mass (e.g. g, kg, t) units. If any one of these parameters is changed the
pulse width may not exceed 50% of the period of the output frequency at 100% flowrate (on/off ratio
1:1). If the pulse width exceeds this limit it is automatically reduced to 50% of the period and the
message Warning! New pulse width is displayed.
Pulse Width
The pulse width (length of the pulses) for the selected pulse output can be set between 0.1 and 2000ms.
The pulse width must be sufficiently short so that at a maximum output frequency (flowrate max. 100%
= 5 kHz) there is no overlapping of the pulses. On the other hand, the pulse width must be long enough
to assure that it can be measured by the connected instrumentation (SPC).
Example:
Flow range = 100 l/min (Qmax = 100 % flow range end value)
Totalizer = 1 pulse/l
100pulses/min
f
= -------------------------------------- - = 1.666 Hz
60s
To allow for a 30% over range
f = 1.666 Hz x 1.3 = 2.166 Hz (1/s)
On/off ratio of 1:1 (pulse width = pause width)
1
t = ----------------------- - x 0.5 = 230 ms
p
–
2,166s
Any value < 230 ms can be set. Counters usually require a pulse width ≥ 30 ms.
The converter automatically checks the pulse width setting. Its maximum value may be 80 % of the
output frequency at 130 % flowrate. If this limit is exceeded, the new value will not be accepted
and the message entry too large will be displayed.
Current and frequency specifications should be considered.
When connecting an active or passive counter the max. allowable current and frequency values must be
considered.
Example:
A passive 24 V counter is connected:
The max. output frequency is 10 kHz.
Voltage
0 V ≤ U ≤ 2 V ; 16 V ≤ U ≤ 24 V
L H
Current
5 mA ≤ I ≤ 30 mA
1