Appendix
Direct actuation of Namur transmitter
(optional)
Selecting a suitable
The correct sensor should always be selected, taking into account the
sensor for rev. speed
structural features of the element to be measured.
monitoring
Since this element is not always known, the following is an approximation
procedure for dimensioning the attenuating elements and selecting a suitable
sensor.
In most cases, a shaft is sensed directly. One or several attenuating elements
(screw-heads or metal plates) are attached directly to the shaft. A symmetrical
arrangement should be ensured, since many instruments work on the principle
of measuring the period , and in the case of more than one attenuating
element require 100% equal intervals between them. If this cannot be
guaranteed, the signal can exhibit jumps (asymmetry can become particularly
noticeable in analogue signals). This problem can be solved by installing only
one attenuating element (this is the standard setting for rev. speed capture in
the FMS).
The illustration (left) shows a typical arrangement of attenuating element,
sensor and shaft.
How the system works:
Every inductive sensor forms an electric field at its active surface, from which
the contact gap (nominal contact gap "Sn”) can be derived as a function of
sensor size. The table lists several typical sensors with their characteristics.
The effective contact gap is 0.8 x nominal contact gap in the case of structural
steel. An additional correction factor that depends on the material must be
included for other materials. These factors are specified in the sensor
manufacturer's data-sheets.
The installation distance between the sensor and the attenuating element's
upper edge should be Sn/2 (half the nominal contact gap). The sensor's
diameter depends on the required nominal contact gap and can be derived
from the table. The attenuating element's diameter should be equal to or
greater than the sensor's diameter (for frequencies < 20% of the sensor's
maximum switching frequency). If the attenuating element is too small, this can
cause problems at high rev. speeds since the element cannot be detected.
The attenuating element's height should be at least 3/4 of the nominal contact
gap. If this value cannot be ensured, the sensor may detect the shaft or it is
pre-attenuated by the shaft to such an extent that reliable rev. speed
measurement cannot be guaranteed. This error too, may become noticeable
only at higher rev. speeds.
Selective list of Turck NAMUR sensors
Typ
sn [mm] sn x 0,8 [mm] D [mm] f [Hz] Installation
Bi1-EG05-Y1
1,0 0,8
5 5.000
flush
Bi1,5-EG08K-Y1
1,5 1,2
8 5.000
flush
Ni3-EG08K-Y1
3,0 2,4
8 5.000
non-flush
Bi2-G12-Y1
2,0 1,6
12 5.000
flush
Ni5-G12-Y1
5,0 4,0
12 2.000
non-flush
Bi5-G18-Y1
5,0 4,0
18 1.000
flush
Ni10-G18-Y1
10,0 8,0
18 500
non-flush
Bi10-G30-Y1
10,0 8,0
30 500
flush
Ni15-G30-Y11
15,0 12,0
30 200
non-flush
145
2xM12
bolted on
Illustration: Example of attaching
an attenuating element (bolt M8)
to the motor shaft's end-face
Original cowling for
the cooling vane or
separate locking frame
