89750147 Crouzet USA, 89750147 Datasheet - Page 230

• Manufacturer Part Number: 89750147
• Description: STAINLESS SLEEVE-MILL TEMP PRB
• Manufacturer: Crouzet USA

Specifications of 89750147

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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230
Tachometers can be used to measure speeds (of linear or rotary move-
ment), rates (per minute or per hour), or rates of flow (volumetric, etc.).
Pulses are fed to the tachometer at the frequency to be measured. A
scale factor is applied to produce readings of the desired type (linear
speeds, flow rates, etc.).
Crouzet/Syrelec tachometers operate on 2 different principles :
1 - The fixed time base principle, and
2 - The reciprocal principle
1 - Principle of the fixed time base tachometer
The tachometer totals the number of pulses received during a fixed per-
iod of time known as the time base. At the end of this period, a value for
the frequency measured is shown on the display.
The time base can be set at the time of installation. It is calculated from
the formula shown below, where :
The time base is given by :
Once the time base has been calculated, it is set by means of DIP
switches (or changeover switches) situated on the unit.
As an example:
2 - Principle of the reciprocal tachometer
This tachometer measures the intervals between n count pulses
(the period) and then performs the calculation
Basic principles of tachometers
to obtain a frequency.
Assume a sensor emits 8 pulses per revolution. What you want to see
on the display is a speed in revs per minute. The maximum this speed
can be is 2000 rpm.
Fixed time base tachometers are useful for high speeds but, if the accu-
racy obtained is to be good, it is essential for the number of pulses per
revolution to be high.
To overcome this drawback, Crouzet Automation can supply reciprocal
tachometers. These need only a single pulse per revolution and are able
to measure both high and low speeds.
General
B
N
N
V
N
N
V = N
d
t
d
t
= 2000
= 8
: is the time base being calculated,
: is the number of pulses per revolution,
: is the number of revolutions per minute, and
: is the value that will appear on the display.
t
(since what you want displayed is a speed in rpm).
B =
f =
2000 x60
1
T
2000x8
B =
Nt xNd
Vx60
= 7,5 secondes
The parameters which govern this tachometer are the following :
The interval between 2 rising edges is very much longer than T r .
The tachometer displays 0 until time T, at which it displays the new value.
Measure-
ment
begins
Measurement ends at the rising edge of the first pulse after T r . If no
pulse is received after T, the system waits until the time limit T
shows zero on the display.
If the frequency of the signal is low, conditions are as shown below :
■
■
Tr
Enables end of measurement
the sampling time (T r )
the time limit for measurement (T
TR
T
TL
Measure-
ment
ends
T
Time limit for
measurement
Pulses e
L
m
)
itted by the sensor
L
and then