Watlow 8LS Controller Setup Guide

Watlow 8LS PID Controller Installation, Programming, and Operation Professional Guide

The Watlow Anafaze 8LS controller is a powerful 1/4 DIN size industrial grade controller designed specifically for complex process control. It provides 8 completely independent PID (Proportional Integral Derivative) control loops, which can directly connect various industrial sensors, including thermocouples (T/C), thermistors (RTD), and infrared non-contact sensors. This guide will provide a detailed overview of the technical specifications, mechanical installation, electrical wiring, programming settings, PID tuning, and troubleshooting methods of the 8LS controller, helping engineers and technicians quickly master the deployment and application of the equipment.

1. Hardware Overview and Core Features

The design of the 8LS controller aims to meet various needs from simple switch control to complex PID regulation. It can operate as an independent controller or be integrated into a computer monitoring system through RS-232 or RS-485 serial interfaces. Its core features include:

Multi loop control: Provides 8 independent PID control loops, each with dual outputs for heating and cooling, suitable for heating/cooling applications.

Flexible sensor input: Supports direct connection to J, K, T, E, N-type thermocouples, as well as RTD and linear voltage/current inputs (with scaling resistors required).

Powerful output capability: The main and secondary outputs of each circuit can be independently configured as time proportional (TP), zero crossing detection (DZC), switch (ON/OFF), or analog output (0-5VDC or 4-20mA).

Comprehensive alarm function: including deviation alarm, high/low process alarm, and global alarm output, which can accurately set dead zone and delay according to process requirements.

Optional advanced features: support for built-in Ramp/Soak programmer for batch processing, and 8LS-CP (carbon potential) function for carbon potential control and furnace gas monitoring.

2. Installation and mechanical requirements

When installing the 8LS controller, it is necessary to strictly comply with safety and regulatory requirements to ensure the reliable operation and long-term stability of the equipment.

Mechanical installation: The 8LS adopts a 1/4 DIN housing design, with standard panel opening dimensions of 92mm x 92mm (height x width). The equipment should be installed vertically on a metal backplate to ensure heat dissipation. In order to ensure the highest accuracy of thermocouple input, the temperature gradient on the housing terminal block should be minimized as much as possible to prevent thermal shock.

Heat dissipation and environment: Ensure sufficient airflow through the housing slot at rated full current output. During installation, avoid being obstructed by other heat sources and ensure that the surrounding environment temperature meets the specifications.

Electrical safety: The power must be cut off before installation. Due to the fact that the input signal of 8LS is not always referenced to ground, there may still be high voltage on the signal line in an unpowered state (such as a thermocouple accidentally short circuiting to the AC power line). After installation, the controller must be placed inside a protective enclosure to prevent operators from coming into contact with live parts.

3. Wiring and electrical specifications

Correct wiring is the key to ensuring measurement accuracy and control stability. The following are detailed wiring requirements and measures to suppress interference.

Analog input wiring:

Thermocouple: Special thermocouple extension wires must be used and routed in their own conduits, away from AC power sources and high-power lines.

RTD: It is recommended to use a three wire RTD (100 Ω platinum resistor) and a multi-core shielded cable.

Linear input: Shielded twisted pair or multi-core shielded cable should be used. For voltage or current input, a scaling resistor must be installed on the 8LS terminal to match the input range of -10mV to+60mV.

Grounding and shielding: The shielding layer of analog signals is usually only grounded on the controller side (120VAC panel ground) or on the sensor side depending on the site conditions. The analog signal ground should be connected to the Analog GND terminal and strictly separated from the logic ground and communication ground.

Control output wiring:

The PID digital output of 8LS adopts optical isolation solid-state relay technology. The radio frequency interference (RFI) generated instantly by the switch when driving the electromechanical relay may cause CPU reset or display failure.

Anti interference measures:

Try to use solid-state relay (SSR) instead of electromechanical relay as much as possible.

Mechanical and electrical relays should not be installed on the same panel as 8LS as much as possible.

Strictly control the circuit and avoid bundling digital output lines with AC power lines.

RC buffer network: This is the most important measure to suppress RFI. Connect a 0.01uF/1000VDC capacitor and a 47 Ω/0.5W resistor in parallel to the normally open (NO) contact of the electromechanical relay coil.

Communication wiring:

RS-232: Used for point-to-point communication (single controller). The maximum recommended length is 3 meters (at 57.6k baud rate).

RS-485: Used for multi station network systems (up to 32 controllers). It is recommended to use shielded twisted pair cables, and the loop resistance of the transmission line (excluding terminal resistance) should not exceed 200 Ω. A 200 Ω terminal resistor must be installed at the end (farthest end) of the line. Recommend using daisy chain connections to avoid star shaped connections.

4. Front panel operation and display

The front panel of 8LS provides an intuitive user interface, making it convenient for engineers to directly monitor and operate on site.

Display mode:

Bar chart display: This is the default power on display, providing an overview of the deviation bar chart for all 8 circuits. The upper and lower limits of the bar chart correspond to high/low deviation alarms, with the set point in the middle.

Single loop display: displays detailed information about a specific loop, including process variables (PV), set points (SP), output percentages, and status (manual/automatic/hold).

Scan display: In single loop display mode, press the YES and NO keys simultaneously, and the controller will automatically cycle through the display of single loop information for all activated loops.

Alarm display: When an alarm occurs, the display will automatically switch to alarm mode and flash the alarm symbol. Press the ALARM ACK button to confirm the alarm.

Function of operation keys:

YES/NO key: used for menu navigation, numerical adjustment, confirmation/cancellation of selection.

BACK key: Return to the previous menu or abort the current editing.

ENTER key: Save data or enter the next level menu.

ALARM ACK key: Confirm alarm, reset global alarm digital output.

MAN/AUTO key: Switch between manual and automatic modes, and adjust the output power in manual mode.

RAMP/SOAK key: used to allocate slope/insulation programs to designated circuits (this function needs to be optionally selected).

CHG SP key: Adjust the set point of the current display circuit.

5. System settings and programming

By setting the menu, users can deeply customize various parameters of 8LS. The settings menu is divided into: global parameters, input settings, control settings, output settings, and alarm settings.

Global parameters:

Controller address: In a multi station communication system, each controller needs to set a unique address (1-32).

Communication protocol: Supports ANASOFT or Allen Bradley protocols.

Communication baud rate: 2400 or 9600.

Slope/insulation time base: Set whether the time unit in the program is "hour: minute" or "minute: second".

Panel lock: prevents unauthorized personnel from modifying parameters through panel buttons.

Power on output status: Set whether the output remains disconnected or returns to its original state after power failure and restart.

Input settings:

Input type: Supports J, K, T, E, and N type thermocouples, RTD1/RTD2， Linear and pulse inputs.

Linear scaling: By inputting high and low process variable values and corresponding instrument readings, the input signal is automatically calibrated to engineering units (such as PSI, m ³/h). For example, entering 100 PSI corresponds to 4mA, and 400 PSI corresponds to 20mA.

Thermocouple offset: used to correct nonlinear errors of specific types of thermocouples (such as J-type) at low temperatures.

Control settings:

PID parameters: The proportional band (PB), integral time (TI), and derivative time (TD) of the heating and cooling outputs can be independently set.

Output type

TP (Time Proportional): The output simulates an analog quantity by changing the on-off time ratio within one cycle, commonly used to drive SSRs.

DZC (zero crossing detection): determines the switch state at the zero crossing of each AC line cycle, especially suitable for fast heating loads (such as open coils).

O/F (switch): Simple on-off control.

ANA (Analog): Standard 0-5VDC or 4-20mA continuous signal.

Output limit: Maximum output limit and limit time can be set for "soft start" or limiting energy input.

Alarm settings:

Process alarm: Independent setting of high/low process alarm.

Deviation alarm: Set the width of the deviation band.

Alarm dead zone: prevents process variables from fluctuating near the alarm value, leading to repeated triggering of alarms.

Alarm delay: Set the duration required for alarm activation to avoid false alarms during startup.

6. PID tuning and tuning

8LS provides automatic tuning function, but in specific applications, manual tuning of PID parameters is necessary.

Control mode:

Switch control: The simplest control, which only activates the output when the process variable exceeds the set range. Suitable for systems with high thermal inertia.

Proportional control: The output is proportional to the error, but there is an offset.

Proportional Integral Control (PI): Introducing an integral term to eliminate static errors.

PID control: Introducing differential terms to eliminate overshoot, suitable for responsive systems.

Automatic tuning:

In single loop display mode, select the control mode as "TUNE", press the ENTER key, the controller will output 100%, and then automatically calculate and set the PID parameters. During the calculation period, if the process variable exceeds 75% of the set point or the calculation timeout (10 seconds), automatic tuning will be aborted.

Universal PID starting value:

Proportional Bands (PB): typically set at 10% (below 1000 ° F) or 5% (above 1000 ° F) of the set point.

Integral time (TI): The recommended starting value is 60 seconds per repetition.

Differential Time (TD): The recommended starting value is 15% of TI.

7. Advanced features: Slope/Insulation

For batch processing applications, the slope/insulation function of 8LS allows users to program multiple temperature curves to achieve precise temperature control programs.

Program structure: A program contains up to 20 segments. Each segment can be set with a time, target set point (slope segment), or maintained at a temperature (insulation segment).

Trigger and Event: Each segment can be configured with external triggers (digital inputs) and events (digital outputs). The trigger must meet the conditions before the segment starts. The event is executed at the end of the segment.

Operation mode:

Run: Execute each section in order.

Maintain: Pause in the current segment, output remains in the final state.

Waiting: Waiting for the trigger signal.

Tolerance error: If the process variable exceeds the tolerance of the segment, the program will enter tolerance preservation.

8. Carbon Potential Control (8LS-CP)

For heat treatment furnaces, 8LS-CP provides special carbon potential and dew point control functions.

Carbon potential control: The 8LS-CP has a built-in high impedance amplifier that directly reads the millivolt output of the zircon carbon probe without the need for an external amplifier.

Probe burnout: This is a crucial step in preventing carbon buildup. Burn off carbon deposits by introducing excess fresh air into the probe.

Program burning: Starting from time or contact, the burning cycle and interval time need to be configured.

Safety mechanism: When the probe temperature exceeds the set limit (such as 1900 ° F), the burn out output automatically shuts off to prevent probe burnout.

Furnace gas alarm: When the reference temperature is not within the range of 1400-2400 ° F, the digital output is activated to cut off the furnace gas supply. The logic of this alarm is different for continuous furnaces and intermittent furnaces (such as intermittent furnaces requiring self-locking function to keep the furnace gas closed until the temperature rises).

9. Troubleshooting

When encountering problems, first diagnose through the status LED and self-test menu on the front panel.

LED status code:

Evergreen: Enable (normal operation).

Flash green: firmware download in progress.

Always red: disabled (no latch error).

Flash red: There is an error, and the number of flashes corresponds to the error code (please refer to the manual).

Red green flashing alternately: undervoltage warning (no AC power supply).

Communication malfunction:

Check the serial cable connection (RX/TX crossover).

Confirm that the baud rate and error check (BCC/CRC) settings are consistent with the host.

For RS-485, check the terminal resistance and common ground connection.

Use a multimeter to check the status of digital inputs and outputs.

10. Conclusion

The Watlow 8LS controller has become a reliable solution in the field of industrial temperature control due to its high-precision multi loop PID control, flexible I/O interface, and powerful programming capabilities. Whether it is simple single loop heating or complex multi-stage batch heat treatment, 8LS can meet stringent process requirements through its rigorous hardware design and rich software tools (such as ANASOFT). Following the installation specifications, wiring standards, and tuning guidelines in this document will help build a safe, efficient, and highly anti-interference control system.