Siemens OCM III, Instruction Manual, Page: 36 / 112

FLOW VELOCITY INPUT
In some applications, the flow calculation for the chosen primary element requires a
velocity input. In this type of application, the transducer measurement is used to
calculate the cross sectional area of the flow. By multiplying the area with the distance
per time units of velocity, the volume per time units of flow are calculated. The
calculated velocity can be viewed via D8.
The 0% and 100% limits of the velocity input must be scaled using parameters
P8 and P9.
» select P8
» enter the voltage corresponding to zero velocity
» select P9
» enter the velocity corresponding to 5 V
e.g. If the velocity sensor output is 1 V per m/sec and the output is
scaled for 7 V at 100% velocity (7 m/sec), then enter 5 m/sec. If the
output is scaled for 4 V at 100% velocity (4 m/sec), enter 5 m/sec.
P8 and P9 can only be accessed if P3 has been set for an option that requires the use
of a velocity input. The input voltage level can be viewed via D12.
AUXILIARY HEAD INPUT
In some applications, the transducer input (TB1-1/2) is not used to provide a signal for
head measurement. A typical example of this is an application which is beyond the 3
m (10 ft) range of the OCM-3. In such a case, the head could be derived from another
Milltronics level monitor or other compatible device.
The method of head determination is set by P42. The OCM-3 simply substitutes the
signal from the auxiliary device for the ultrasonic measurement provided by the
transducer. The programming and consequent flow calculation are performed
as normal.
typical 1 - 5 V signal from
velocity sensor.
typical 4 - 20 mA signal from velocity sensor.
Add terminating resistor.
e.g. 250
Ω
for 1 - 5 V over 4 - 20 mA.
Current Input
Velocity Input
(additional to Basic Wiring)
Signal must be positive with respect to ground.
Voltage Input
7ML19985AB01 OCM III 36