Alicat VC Series Volumetric Flow Controller - Manual (Page 7)

7
Input Signals
Analog Input Signal
Apply analog input to Pin 4 as shown in Figure 1.
Standard 0-5 Vdc: Unless ordered otherwise, 0-5 Vdc is the standard analog input signal. Apply the
0-5 Vdc input signal to pin 4, with common ground on pin 8. The 5.12 Vdc output on pin 2 can be wired
through a 50K ohm potentiometer and back to the analog input on pin 4 to create an adjustable 0-5 Vdc
input signal source as shown below.
7 6
5 4 3
2 1
8
5.12 Vdc
50 KOhm
Potentiometer
0-5 Vdc
Figure 2. Simple method for providing set-point to controllers
Optional 0-10 Vdc: If specified at time of order, a 0-10 Vdc input signal can be applied to pin 4, with
common ground on pin 8.
Optional 4-20 mA: If specified at time of order, a 4-20 mA input signal can be applied to pin 4, with
common ground on pin 8. Note: 4-20mA output requires at least 15 Vdc power input.
RS-232 Digital Input Signal
If you will be using the RS-232 input signal, it is necessary to connect the RS-232 Output Signal (Pin
5), the RS-232 Input Signal (Pin 3), and Ground (Pin 8) to your computer serial port as shown in Figure
3. Adapter cables are available from the manufacturer or they can be constructed in the field with parts
from an electronics supply house. In Figure 3, note that the diagrams represent the “port” side of the
connections, i.e. the connector on top of the meter and the physical DB-9 serial port on the back of the
computer. The cable ends will be mirror images of the diagram shown in Figure 3. (See page 21 for
details on accessing RS-232 input.)
Output Signals
Note: Upon initial review of the pin out diagram in Figure 1 (page 6), it is common to mistake Pin 2
(labeled 5.12 Vdc Output) as the standard 0-5 Vdc analog output signal! In fact Pin 2 is normally a
constant 5.12 Vdc that reflects the system bus voltage and can be used as a source for the input signal.
This allows the user in the field to run this output through a 50K ohm potentiometer and back into the
analog set-point pin to create a 0-5 Vdc set-point source.
RS-232 Digital Output Signal
If you will be using the RS-232 output signal, it is necessary to connect the RS-232 Output Signal
(Pin 5), the RS-232 Input Signal (Pin 3), and Ground (Pin 8) to your computer serial port as shown in
Figure 3. Adapter cables are available from the manufacturer or they can be constructed in the field with
parts from an electronics supply house. In Figure 3, note that the diagrams represent the “port” side of