Measurements With External Input - Chauvin Arnoux C.A 1725 Notice D'utilisation

3.3 MEASUREMENTS WITH EXTERNAL INPUT

The device has a 4-contact connector that can be used to connect an external source of which you
wish to measure the speed, the frequency, the period, the duty cycle, etc.
In order to inform the tachometer that the measurement is available on the external input, it is necessary
to short-circuit contacts 1 and 4.
Operation using the external input is indicated on the display unit by the extinction of the transmission
symbol and the display of EXT.
Wiring
Connector of the tachometer
seen from contact side
Connecting 1 to contact 3 makes it possible to adapt the triggering threshold to the nature of the signals.
Contacts 1 and 3 not connected
For operation with 0 - 5V TTL signals.
The triggering threshold is +1.1V (at 1kHz).
To avoid the problems due to noise often present in an industrial environment, the threshold has a
hysteresis of 250mV.
Contacts 1 and 3 connected
For operation with signals balanced with respect to earth.
This function allows direct measurement using a variable-reluctance magnetic sensor or the output of
an alternator.
The triggering threshold is 300mV (at 1kHz), with a hysteresis of 250mV. The residual noise superimposed
on the signal to be measured must be less than 250mV so as not to interfere with the measurement
when the threshold is crossed.
ATTENTION :
The maximum voltage to input no. 2 must not exceed ± 20Vp. The earth of the external input
connected is electrically connected to the earth of the USB digital output.
The external input must be used for the measurement of slow signals, from 0.1Hz. The table below
sums up the characteristics of this input.
1- earth
2- measurement input (± 20VC max.)
3- see below
4- to be short-circuited with contact no.1
38