8.1
Differential level measurement
Fig 8.1 shows the Silometer differential level measurement function, Fig. 8.3 a typical
application taken from wastewater management. The two capacitance probes measure
the difference in levels h
2
- h
1
,
∆
h, which is used to control the inclination of the rake. A
continuous display of level h
1
is provided at output 1 and of
∆
h at output 2. The level
measurement at output 1 can be used to provide a flow measurement when an
appropriate linearization table is entered for channel 1. When probe 1 is located
downstream of probe 2, the level difference is indicated as a positive value
Calibration
The system is calibrated on-site. The following parameters and actions are required:
•
Sensor constants »f
o
« and »S« from the electronic insert - see Section 2.1.
•
Regulation of level to give minimum and maximum for both probes.
Preliminaries
Step
Matrix
Entry
Significance
1
V9H5
671
Reset transmitter
2
-
»E«
Register entry
3
V8H0
3
Select operating mode 3, »differential measurement«
4
-
»E«
Register entry
Sensor adjustment
Step
Matrix
Entry
Significance
1
V3H5
e.g. 99.5
Enter zero frequency »f
o
« for probe 1 (channel 1)
2
-
»E«
Register entry
3
V3H6
e.g. 1.056 Enter »S« value of probe 1
4
-
»E«
Register entry
5
V7H5
e.g. 98.8
Enter zero frequency
»f
o
« for probe 2 (channel 2)
6
-
»E«
Register entry
7
V7H6
e.g. 1.056 Enter »S« value of probe 2
8
-
»E«
Register entry
BA064E43
Probe 2
Channel 2
Motorized
rake
Probe 1
Channel 1
Output 2
∆
h = h
2
-h
1
Output 1
level 1
Relay 1,
level 1
Relay 2,
rake control
Fig. 8.3:
Example for differential level
measurement:
level regulation through
motorized rake.
Silometer FMC 672 Z/677 Z
Chapter 8: Other Applications
42
