100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
User Guide
Page 125
HA028910
Issue 13 Sep 16
4.3.11 FUNCTION (Cont.)
RATE-OF-CHANGE
The equation solved is:
Where:
dPV/dt = Rate of change of PV with time
In
t
= Input value ‘this time’
In
t - P
= Input value ‘last time’ (i.e. ‘this time’ – P)
P = Sample period (i.e. ‘this time’ – ‘last time’) in seconds. Only periods that are a multiple of
0.125 seconds are accepted.*
R = Scaling factor. Generally, R is the number of seconds in the required ‘per unit time’ value.
For example: if R = 1, the rate is ‘per second’; if R = 60, the rate is ‘per minute’; if R = 3600,
the rate is ‘per hour’.
*Note: For channels being read over Modbus, the ‘priority intervals’ set in the Modbus Master
confi guration menu (section 4.3.16) may cause the readings to be inaccurate or to be continuously
zero. For this reason, a minimum sample period of 1 second is recommended.
Figure 4.3.11n Rate of change confi guration menu
Function
Rate of change of
Sample period
Rate Scalar
Units
Maths Number
Value
Units
s
Apply Discard
Reset now
Rate of change
0.125
Units
1) Channel 1
0.125
1) Math 1
0.0000
dPV
dt
!
In
t
"
In
t
"
p
P
$
R
