4
BASIC OPERATION
The T48 controls a process temperature by measuring the temperature via an
input probe, then calculating a control output power value by use of a modified
PID control algorithm. The unit controls the system with the new output power
value to keep the process temperature at setpoint. The PID control algorithm
incorporates features which provide for high control accuracy and low
temperature overshoot from process disturbances.
FRONT PANEL FEATURES
In the normal operating mode, the unit displays the process temperature
in the upper display. One of the following parameters can be viewed in the
lower display:
- Setpoint
- % Power Output
- Temperature Deviation
- Heater Current
- Temperature symbol (F or C)
- Blank Display
The user scrolls through these parameters by pressing the D button. If
enabled, the control setpoint or power output (manual mode only) can be
directly modified in this mode.
In the normal operating mode, parameters are selected by use of the P button
and modified by use of the UP and DOWN buttons. Parameters are then entered
by the P button, which advances the user to the next parameter. Pressing the D
button immediately returns the controller to the normal operating mode without
changing the currently selected parameter.
HARDWARE FEATURES
A fast 100 msec input sampling rate provides quick controller response to a
process disturbance, thus providing excellent temperature control. Measurement
accuracy of 0.3% of span ±1°C or better, provides close process control
conforming to the desired control setpoint value. The T48 accepts a variety of
both thermocouple and RTD temperature probes. An output board contains the
Main Control output, Alarm 1 output, Alarm 2/Cooling output, and/or Linear
DC output. Since the controller is serviceable from the front of the panel, the
output board (on some models) may be easily changed or replaced without
disturbing the wiring behind the panel. No re-programming is required when
changing or replacing the output board for units without the Linear DC output
option. Units with the linear output option require calibration procedure for the
new linear output.
Low-drift, highly stable circuitry ensures years of reliable and accurate
temperature control. The recommended two year re-calibration interval is easily
accomplished via the programming menu.
REMOTE SETPOINT INPUT
The remote setpoint input facilitates the use of a remote signal to drive the
controller’s setpoint. The remote signal can be scaled independent to that of the
controller’s range. The controller’s response to local/remote setpoint transfers
can be programmed. Also, the remote signal is filtered by use of an adaptive
filter. With this filter, relatively large filtering time constants can be used
without suffering from long settling times. The time constant and filter disable
band are programmable. Additionally, the remote signal can also be velocity
limited (or ramped) to slow the controller’s response to changes in setpoint. This
results in a steady control response with no overshoot.
HEATER CURRENT MONITOR
The T48 provides a direct readout of process heater current. This provides
valuable information regarding single phase heater system integrity. It is
especially useful on extruder and large oven applications where adjacent
controllers mask the effect of a failed heater. The heater break alarm senses two
types of heater system faults:
1) Main control output is “on” and heater current is below alarm value. This
indicates failed heater or failed parts of heater, breaker trip, failed power
control device, etc.
2) Main control output is “off” and heater current is above 10% of alarm value.
This indicates a failed power control device, wiring fault, etc.
LINEAR DC ANALOG OUTPUTS
The Main Linear DC output has independent scaling, programmable output
update time and filter (damping) time. These parameters permit flexibility in
process configuration. The output can be set for 0 to 10 V, 0 to 20 mA or 4 to
20 mA ranges, and can be configured for control or for transmission of
temperature or setpoint values.
A Second Linear DC output is dedicated for retransmission of input
temperature. The output can be scaled and converted independent of the input
and Main Linear DC output. This output is isolated from the input.
SETPOINT FEATURES
The controller setpoint can be protected from out of range values by
programming the setpoint range limit values. Additionally, safeguards from
inadvertent data entry can be programmed.
A second setpoint value can be programmed which can be made active by a
user input and/or through the front panel on selected models.
The setpoint ramp feature ramps the setpoint value at start-up or any time a
setpoint change is made, at a user programmable rate. This feature reduces
thermal shock to the process and helps to minimize temperature overshoot.
INPUT FEATURES
A programmable input filter can be used to stabilize readings from a process
with varying or oscillating temperature characteristics, helping to provide better
temperature control. A programmable temperature shift function can be used to
compensate for probe errors or to have multiple T48 units indicate the same
nominal temperature.
The programmable User Input can be used to control a variety of functions,
such as auto/manual transfer of the controller, reset alarm output
(s)
, transfer to
second setpoint, etc.
OUTPUT FEATURES
Programmable output power limits provide protection for processes where
excessive power can cause damage. Automatic sensor probe break detection,
for fail-safe operation, causes the controller to default to a programmed output
power (upscale or downscale burnout). Programmable output cycle time,
output hysteresis and dampening can reduce output activity without degrading
control accuracy. The main outputs can operate in PID, ON/OFF, or manual
control modes.
CONTROL AND ALARM OUTPUTS
In addition to the Linear DC outputs, there are up to three types of ON/OFF
outputs.These outputs can be relay, logic, or triac for control or alarm purposes.
Relay outputs can switch user applied AC or DC voltages. Logic/SSR drive
outputs supply power to external SSR power units. One Logic/SSR Drive output
can control up to four SSR power units at one time. The Triac output supplies
one Amp of AC current for control of an external AC relay or triac device.
AUTO-TUNE
The T48 has an auto-tune feature which, on demand, automatically
determines the PID control parameters for a particular thermal process. After
completion of auto-tune, the PID parameters are automatically optimized for
that process and loaded into non-volatile memory. The operator may view and
modify the parameters as desired.
Auto-tune may be invoked either at start-up or at setpoint, depending on the
process requirements. An auto-tune programmable dampening factor produces
various levels of process control and response characteristics.
RS485 Communications
The RS485 communications option allows the connection of up to 32 devices
on a single pair of wires with a distance of up to 4,000 feet and a maximum baud
rate of 9600. Since the same pair of wires are used for both transmit and receive,
only one way communication is possible at any given time. The controller has
a programmable response time to allow the host device adequate time to release
the communication line for a transmission.
Selected parameters from the T48 can be interrogated or changed, and alarm
output(s) may be reset by sending the proper command code via serial
communications. It is also possible to invoke Auto-tune through the serial port.
Serial communications used with SFCRM software allows for easy controller
parameter configuration by computer.
HEATING AND COOLING SYSTEMS
The T48 is available with dual outputs to provide heating and cooling to those
processes that require them. For example, many extruder applications require
both heating and cooling to maintain accurate extruder barrel and die
temperatures. The T48 is easily configured for these types of applications.
