Tflow – Yokogawa RotaMASS 3-Series User Manual

Page 163

7. pArAMETEr dESCrIpTION

7-91

IM 01R04B04-00E-E 8th edition March 01, 2011 -00

10% higher is recommended because the duty
cycle is not always exact 50%. For certain pulse
widths the duty cycle at max.Q is larger than 50%
so fewer pulses can be generated. These pulses
are delivered later when the flowrate is again
below max.Q minus 10%. To avoid this situation it
is recommended to keep the flowrate always 10%
below max.Q.
Example :

Flowrate : 11 t/h

Pulse unit : kg

Pulse rate : 0.1 kg/P

Time factor (related to s) = 3600 P/h

Check :

Lowest pulse width

= 0.5 s*pulse rate* time factor/ max. flow rate

= 0.5 s*0.1 kg/P *3600 P/h /(11000 kg/h)

= 16.4 ms

→ customer should select 10 ms pulse width or lower.

Max. Q = 18000 kg/h

11000 kg/h < 18000 kg/h - 10%

result :

Pulse width = 10 ms

Pulse rate = 0.1 kg/P

For a first orientation the max. Q for certain pulse
widths and units for a pulse rate of 0.1, 1 and 10
are given in the table 7-1.

Max. flow restriction :

Set as a pulse output the pulse length is constant
but the time between the pulses varies. Even at
constant flow the time between the pulses might
vary because the microprocessor has to find a
suitable gap in its timing to send the pulse.
Typical pattern for frequency output :

Typical pattern for pulse output
(50 ms; 0.1 kg/P; 2580 kg/h) :

Setting the pulse output
Because the duty cycle of pulses is max. 50%,
the max. flowrate is restricted by the pulse width,
the unit and the pulse rate :
Max. flow rate =
1s/(pulse width*2) *pulse rate *time factor
Example :
Max. Q should be calculated in kg/min
Pulse width = 50 ms
Pulse rate = 0.1 kg/P
Time factor (related to s) = 60 P/min
Max. Q = 1s/(0.05s *2) *0.1kg/P * 60P/min = 60kg/min

If the flow is higher than max.q pulses will be
lost. Therefore it is mandatory to choose the
pulse width/rate so, that the calculated max.
q is always 10% higher than the maximum
expected flowrate.

flow

Max flow from pulse width, unit, rate

this amount will
be lost

flow

Max flow from pulse width, unit, rate

Grey zone

this amount will
be lost

F3.EPS