DESIGNER’S HANDBOOK 4189350049C EN
Page 81 of 206
5.7.3.2 Recommended sensor types
For the practical test of the DX1 RPM function, we have used two different inductive sensors from BALLUFF
sensor.
•
NPN type: BES 516-329-BO-C-02 BES01EF, normally open, 2 mm sensing distance
•
PNP type: BES 516-325-BO-C-02 BES01AZ, normally open, 2 mm sensing distance
The full specification of the tested sensors can be found
on
and can be a useful reference for
selecting a suitable RPM pickup sensor to use with
DX1.
The sensor tests were performed using a specially
constructed RPM test machine with a rotary disc where
16 bolts were equally distributed around the edge. One
or two pickups can be mounted depending on the
actual test, see picture. The test machine is able to
rotate the disc at a maximum speed of 5250 RPM, and
with 16 bolts this equals a max frequency of 1400 Hz.
For unidirectional RPM measurements (direction independent) only one sensor is used.
For bidirectional RPM measurements both sensors are used. In this case, the sensors are mounted with a
mechanical offset, meaning that the pulses from the sensors are also offset in time, making it possible to determine
the direction of the movement.
5.7.3.3 Mechanical RPM system recommendations
The mechanical RPM pickup system can be made in
several different ways, either with bolts passing the
inductive sensor or using a disc with a number of cut-
outs along the edge to activate the inductive sensor
(see picture).
It is recommended to use a high number of bolts (or
cut-outs) in the disc as possible to obtain the highest
possible RPM resolution, but keep in mind that the
frequency at max RPM does not exceed the max rating
on the pickup sensor or the DX1 input.
The following table contains a guideline for number of bolts or cut-outs dependent on the max. rotation speed.
Max RPM range Number of
bolts
(or cut-outs)
RPM
resolution
Max frequency
<100
20
0.05
33 Hz
100 to 500
10 to 20
0.05 to 0.10
16.7 to 167 Hz
500 to 5000
6 to 10
0.10 to 0.167
50 to 833 Hz
To get the best possible performance it is important to position the bolts (or cut-outs) with high accuracy on the disc
and mount the disc on the shaft using a stable construction to reduce jitter on the measurements.
Less than 3 bolts or cut-outs on the disc are not recommended.
