8.6.1.COVOL
This input is designed for a potential free contact between terminals 1 & 2 of the
connector. Terminal 1 is connected to the common of the instrument. This input
has a 1 M
ȍ
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
The turbine input is designed for connecting to the coil of a magnetic pick-up.
The input impedance is 1,2 K
. 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.
1 M
2
1
+3.3V
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 situated below the bush buttons
on the opposite side of the PCB. The right hand side terminal is the positive (+) and the
left hand side terminal is the negative (-).
100
1K
100
2
3
Pick-up
Host or
Power Supply
CH420
+
+
-
-
Complies with the Directive EMC 89/336/EEC
7
