<6. ELECTRONIC TRANSMITTER (-E)>
6-18
IM 01R01B02-00E-E 12th edition October 01, 2014 -00
All Rights Reserved. Copyright © 2003, Rota Yokogawa
6.2.14 Float blocking indication (F7-)
6.2.14.1 Function
Float
Pulsating movements of the flow medium (gasses, liquids) lead to fluctuations of the float and with that to
fluctuations of the tap system/pointer. Therefore the electrical measuring signal permanently changes and with
that the display value and the output current value.
The fluctuations can be reduced with the help of the damping function “F21”. That shows however that the
medium still flows and the float/the tap system is not blocked. This means that in most applications there is a
permanently changing measuring signal which can be used for the recognition of the movement or the
blockade of the float.
Basic noise
Since it is an electronic evaluation circuit, permanently minimal fluctuations of the measuring signal appear. The
basic noise is caused by vibrations in the plant as well as by temperature influences or external magnetic
fields. The basic noise also appears, if
- no medium flows through the measuring pipe
- the float and with that the tap system are in the rest position
- the float/the tap system is blocked.
Float-Blocking-Indication
The function of the Float-Blocking-Indication allows the electronic transmitter to distinguish the fluctuations, which
are caused by a moving float, with the fluctuations of the basic noise to state a fault status. If the measuring
signal does not exceed the autozero value during a defined supervision time, this is recognized as blockade
and an error condition is shown.
6.2.14.2 Operation
Switching on
At delivery of the equipment the Float-Blocking-Indication is turned off. By the function “F71 2” the Float-
Blocking-Indication can be activated.
Autozero function
The autozero function is called to find out the level of basic noise in the application. This is started with the
function “F74 1” and lasts for 90 seconds. While the autozero function is running the value “0.000” is displayed
and the 4 bars will flash below the numbers. After approx. 80 seconds the current autozero value appears on
the display. This value gets stored and will not be lost after power off / on the RAMC or after switching off / on
the Float-Move-Detection-function. The stored value is typed over first after a renewed autozero.
Autozero without flow
To execute the autozero function the following expiry is recommended:
- Plant in operation (measuring tube filled with medium)
- Drive flow to zero (place float into rest position)
- Raise the pointer to 10% to 20% of the flow and fix it on the scale with adhesive tapes or underlayed paper
stripe .
- Start Autozero function by menu.
- Check Autozero value after approx. 80 seconds.
During the Autozero function it absolutely has to be respected that:
- the RAMC is not moved by touching or using the 2 buttons.
- the pointer is protected against slipping.
- the tube is not exposed to strong tremors
If these prerequisites are not adhered, it comes to the inquiry of too high autozero results.
This leads that a relatively quiet flow can trigger the Float-Blocking-Indication.
