66
Fig. 37: Driving the control input
6.10
Setting the system control
Some applications for the MFM 2081 and MFM 3081 may require measurement to be
suspended at particular times, such as during steam cleaning. The system control functions
allow the converter to automatically detect user-defined conditions and then to act accordingly.
Selectable conditions (Fct. 3.7.2.) are :
Density out of range
Temperature out of range
The ranges for these conditions are set by Fct. 3.7.3. and 3.7.4. (These range checks are
subject to hysteresis in the same way as the process alarm, see Sect. 6.7).
When such a condition is met, the converter takes one of the following actions :
1. Flow reading forced to zero, totaliser stopped, any output registering flow will go to zero.
2. Flow reading forced to zero as above, but totaliser is cleared to zero when measurement
restarts.
3. Disable outputs. All outputs, current, frequency and alarm are forced to their zero/inactive
state.
Example:
A process has to be steam cleaned regularly. The user has the pulse output set to total mass,
but he does not want pulses sent to his instrumentation during cleaning. However, he still
requires a temperature reading from the current output. The nominal density of his process
fluid is 1.2g/cm3.
