Table of Contents
Advertisement
9.1
Input characteristics
NOTE: The input terminals are not isolated from the 4-20 mA loop. Under no circumstances
can an electrical connection be made between the 4-20 mA loop and the inputs. In the event
of supplying various transmitters with the same power supply one must make sure that the
inputs isolated between each other (except the shields of the turbine pick-ups which can be
connected together).
9.1.1
COVOL input characteristics
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 MΩ pull-up
resistor connected to terminal 1 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
9.2.2
TM input characteristics
The turbine input is designed for connecting to the coil of a magnetic pick-up.
The input impedance is 1,2 kΩ. This input is protected to limit the maximum 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 frequency is 0.06 Hz.
The minimum input voltage is 7mVpp.
11
Advertisement
Table of Contents
