model 2704 controller installation and operation handbook - Soliton

Standard IO
2704 Controller
17.4. THE FIXED RELAY OUTPUT PARAMETERS
Allows access to parameters which set up the fixed Relay output connected to terminals AA,
AB and AC. This relay may be used as an alarm relay. or a time proportioning control
output.
17.5. TO SCALE THE FIXED RELAY OUTPUT
If the relay is used as a time proportioning control output this means that the relay will, by
default, be fully off for 0% power demand, fully on for 100% power demand and equal on/off
times at 50% power demand.
As with input scaling you can change these limits to suit the process. It is important to note,
however, that these limits are set to safe values for the process. For example, for a heating
process it may be required to maintain a minimum level of temperature. This can be achieved
by applying an offset at 0% power demand which will maintain the relay on for a period of
time. Care must be taken to ensure that this minimum on period does not cause the process to
overheat
These offsets can be made to parameters in the ‘AA Relay’ pages. The above example is
shown in Fig 17-2
PID Demand
signal
Eng Value Hi
eg 100%
Eng Value Lo
eg 0%
Electrical Lo
eg Relay on for
short period
Electrical Hi
eg Relay
permanently on
Electrical Output. In
this example the
on/off ratio of the
output relay
Table 17-2: Fixed Relay Scaling
17-8 Installation and Operation Handbook. Part No HA026502 Issue 1.0 Apr-00