8.6.1.COVOL
If the Pulse input is configured for Covol (jumpers in position 2-3), a potential free
contact can be connected between terminals 1 & 2. Terminal 1 is connected to the
common of the instrument. This input has a 1 M
Ω
pull-up resistor connected to
terminal 2 and to the 3,3 V power supply. The input has a hysteresis with the
switching points situated at about 1 V & 2,1 V. If an open collector transistor is to
be used as the switching element instead of a COVOL, then the aforementioned
parameters must be taken into account.
Due to the presence of a filter to avoid the effects of contact bounce, the maximum
pulse frequency for the COVOL input is 300 Hz.
The minimum input frequency is 0.06 Hz
8.6.2 .Turbine
If the Pulse input is configured for Turbine (jumpers in position 1-2), a coil of a
magnetic pick-up can be connected between terminals 1 & 2.
The input impedance is 1,2 K
Ω
. This input is protected to limit the maximun applied
voltage to the circuit. This protection consists of two diodes in parallel and two 100
Ohm resistors.
The maximum voltage that can be applied to the input is 10 Vpp. Voltages higher
that this can cause damage to the equipment.
The maximum input frequency is 5000 Hz
The minimum input voltage is 7 mVpp
8.7. Loop connection
The 4-20 mA loop is connected to a screw terminal block marked as
mA
. The right hand
side terminal is the positive (+) and the left hand side terminal is the negative (-).
Host or
Power Supply
CH420
+
+
-
-
Complies with the Directive EMC 89/336/EEC
7
1 M
2
2
1
1
+3.3V
100
1K
100
2
2
1
3
Pick-up
