Watlow Series 942 Controller

Automatic tuning (recommended)

Applicable scenario: Quickly obtain optimized PID parameters after first use and system load changes.

Operation steps:

Enter the Operation menu and find the Aut parameter (displayed only when Ot1=ht).

Press the UP/DOWN keys to select the tuning rate (1 slow/2/3 fast, mostly 2 in most scenarios).

Press the MODE key to start tuning, and the lower display alternately flashes Aut and the current parameter. During tuning, the cooling output is turned off, and the heating output runs at 90% set point ON/OFF.

Complete tuning within 80 minutes, automatically save PID parameters, restore Aut to 0, and return to normal control mode; Modifying the set point during tuning will restart tuning. Press the UP/DOWN key to set Aut=0 to abort (restore the original parameters).

Manual tuning (precise optimization)

Operation steps:

Initialization parameters: Pb1=1, Ct1=5, rE1=rA1=0, CAL=0, Aut=0, set target temperature.

Proportional band (Pb1) adjustment: gradually increase Pb1 until the process temperature stabilizes (initial reset to 0, temperature may deviate from the set point).

Reset/Integral (rE1) Adjustment: Gradually increase rE1 until the temperature begins to oscillate, then slowly decrease until the temperature stabilizes near the set point.

Rate/Differential (rA1) Adjustment: Assuming rA1=1.00 minutes, raise the set point by 20-30 ° F. If the temperature is overshoot, increase rA1 (maximum 9.99) to avoid overshoot and slow response.

Cycle time (Ct1) adjustment: Optimized within the range of 1-60 seconds. It is recommended to choose a longer cycle time for mechanical contactors (to reduce wear) and a shorter time for electronic loads (to improve control accuracy).

Alarm and fault handling

Alarm function operation

Alarm type:

Process alarm (Pr): Based on the absolute temperature threshold (A1LO/A1HI), an alarm is triggered when the temperature exceeds the range.

Deviation alarm (dE): Based on the set point offset (such as+7 ° F/-5 ° F), the alarm threshold synchronously shifts when the set point changes.

Alarm status:

Non Locked (nLA): Automatically resets after the alarm condition disappears.

Lock (LAt): Manual reset is required (first eliminate the alarm condition, then press the HOLD/RUN button).

Alarm indication: The lower display alternately flashes "LO"/"HI" and the current parameter, the L3/L4 LED lights up, and the auxiliary output triggers (N.O. closed/N.C. open).

Common faults and solutions

Fault symptoms, error codes, possible causes, and solutions

The upper display shows "----", the lower display shows Er7 Er7 A/D overflow, the sensor is open/polarity reversed, check the sensor wiring (positive and negative poles, terminal contact), confirm that the In parameter is consistent with the sensor type

The upper display shows "----", the lower display shows Er1/Er2 Er1/Er2 sensor over/under range, A/D fault confirms that the sensor range matches rL/rH, checks if the sensor is damaged, and recalibrates the A/D

Pause during program operation - gSD deviation window enabled, adjust gSD value if temperature exceeds ± gSD range (increase window), check if heating/cooling system is normal, eliminate load interference

Communication failure - baud rate/protocol/address mismatch, wiring error. Confirm that bAUd (baud rate), Prot (protocol), Addr (address) in the Setup menu are consistent with the host, and check the communication line wiring (RS-485 requires corresponding A/B lines)

Large temperature measurement error - sensor wiring error, calibration offset, environmental interference. Reconnect and confirm sensor type, enter Cal menu to adjust CAL offset, check signal line shielding and grounding

Output unresponsive - Set the set point to OFF, configure the output type incorrectly, adjust the SP to the rL~rH range for load faults, confirm the Ot1/Ot2 parameters (ht/CL), check if the load impedance matches the output type, and test if the load is normal

Calibration operation (accuracy calibration)

Calibration prerequisite

Only enter under LOC parameters and require precise equipment (such as precision millivolt source, resistance box, voltage/current source, 4.5-inch multimeter).

Backup all parameters (Setup/Operation/Program) before calibration, turn off all outputs during calibration (except for process outputs), and automatically save calibration values when the RUN LED lights up.

Core Calibration Process (Taking Thermocouples as an Example)

Wiring: Connect the precision millivolt source to terminals 7 (+) and 9 (-), connect to AC power and ground.

Preheating: Power on for 15 minutes, enter the Cal menu (hold down the UP/DOWN key under LOC parameters), press the MODE key to select the tCL parameter.

Low range calibration: The millivolt source outputs 0.00mV, and after stabilizing for 10 seconds, press the MODE button.

High range calibration: J-type thermocouple outputs 50.00mV, R/S/B type outputs 16.035mV. After stabilizing for 10 seconds, press the MODE button.

Compensation calibration: Disconnect the millivolt source and connect the J-type reference compensator (32 ° F/0 ° C). After stabilizing for 10 seconds, press the HOLD/RUN button to exit the RUN mode and complete the calibration.