Figure 28 - Material Selection Using Digital I/O - Hydronix Hydro-View HV02 User Manual

SENSOR CONNECTIONS – HYDRO-PROBE I
A multiplexing method is used by the Hydro-View to determine the state of the two
external switches SW1 and SW2 and thus to determine which material calibration table to
use. These 'switches' may of course be 'outputs' from a control system; however, they
must be of the 'voltage-free' type for the scheme to operate correctly. The diagram above
shows the internal excitation supply being used, but an equivalent arrangement for
external excitation is possible.
The multiplexing sequence performed by the Hydro-View is as follows...
The Hydro-View requires that the state of switches SW1 and SW2 remain stable for two
multiplexing cycles before it updates its internal values. To avoid excessive wear on the
Hydro-View relay contacts, this process takes about 5 seconds to complete and thus the
external control system should allow sufficient time for any changes of material to be
propagated to the Hydro-View.
The material table number corresponding to the states of switches SW1 and SW2 is given
by...
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HYDRO-VIEW USER GUIDE D0022 REV 1.06
Figure l-4 Material selection using digital I/O
•
⇒ Close relay output on terminal 20 and open relay on terminal 21.
⇒ Read state of SW1 on terminal 15.
⇒ Open relay on terminal 20 and close relay on terminal 21.
⇒ Read state of SW2 on terminal 15.
⇒ Repeat from beginning as required.
SW2 SW1 Material table
Open Open 1
Open Closed 2
Closed Open 3
Closed Closed 4