User`s manual

535 User's Manual Chapter 7 95
Applications
When the target setpoint is being shown, RAMPING will not appear. Pressing
the DISPLAY key will scroll the 2nd display as follows:
• From the target setpoint to the actual (ramping) setpoint;
• To the deviation from setpoint;
• To the output level; and
• Back to the target setpoint.
Note that when ramping, the deviation indication is with respect to the target
setpoint.
The ramp-to-setpoint function is triggered by one of three conditions:
1. Upon power up, if the 535 powers up in automatic control, then the setpoint
will ramp from the process variable value to the setpoint value at the specified
rate.
2. On a transfer from manual to automatic control the setpoint will ramp from
the process variable value to the setpoint value at the specified rate.
3. On any setpoint change, the setpoint will ramp from the current setpoint to
the new target setpoint. When triggered, the display will automatically change
to indicate the ramping setpoint.
Software Configuration
1. Go to the PV INPUT menu.
2. Set the SP RAMP parameter to the desired rate of change.
O. INPUT LINEARIZATION
Thermocouple and RTD Linearization
For a thermocouple or RTD input, the incoming signal is automatically linearized.
The 535 has lookup tables that it uses to provide an accurate reading of the
temperature being sensed.
Square Root Linearization
Many flow transmitters generate a nonlinear signal corresponding to the flow
being measured. To linearize this signal for use by the 535, the square root of
Figure 7.16
Square Root Linearization Formula
PV = Low Range + [ (Hi Range – Low Range) (V
input
- V
low
/ (V
high
– V
low
) ]
Hi Range is the high end of the process variable.
Low Range is the low end of the process variable.
V
input
is the actual voltage or current value of the input.
V
high
is the high end of the input signal range (e.g. 5 volts or 20 mA).
V
low
is the low end of the input signal range (e.g. 1 volt or 4 mA).
Example:
PV range is 0 – 1000.
Input signal range is 1–5 volts.
Input signal is 3 volts.
Therefore PV = 0 +
[ (1000 – 0) (3-1) / (5–1) ] = 1000 .5 = 707