CLS200 and MLS300 Cascade Control Setup and Tuning of CascadeFunctions

Loop 1, select Loop 1. 

Second, the Base SP, Min SP, Max SP, and Heat Span, and Cool Span parameters need to be set. All parameters are

in the engineering units of the Control Loop or Secondary Loop.

If the process is controlling a process with a SP at 140°F and at -22°F while not wanting any control output at 

ambient, which is consider to be 75°F, the following will apply. 

BASE SP = 75, this is the base value at which all other values will be referenced from. This value must be set 

whenever using heat, cool, or heat and cooling control outputs. 

Min SP = -35, this is the value at which the lower SP value cannot exceed and must be greater than the cooling SP 

of -30. This value can be set to the input range lowest value, if desired so that it would not need to be included in 

any future resetting of cascade parameters. 

Max SP = 145, this is the value at which the higher SP value cannot exceed and must be greater than the heating SP 

of 140. This value can be set to the input range highest value, if desired so that it would not need to be included in 

any future resetting of cascade parameters. 

Heat Span = 65, this is the value which is the span between the Base SP and the desired heat SP. i.e. 140 – 75 = 65. 

This is the value that must be set if using heat only or heat and cooling outputs as well as the Base SP. 

Cool Span = 105, this is the value which is the span between the Base SP and the desired cool SP i.e. -75 + -30 = 

105. This value must be set when using heat and cooling or cooling only outputs as well as the Base SP. 

Heat only example: Low SP = 1200 and High SP =1600. 

Base SP = 1200 and Heat Span = 400. 

Cool only example: High SP = 50 and Low SP = 30. 

Base SP = 50 and Cool Span = 20 

Watlow Winona OH 07/28/06 

1241 Bundy Blvd 

Winona, MN 55987 

Telephone (507) 494-5656 

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© 2005 Watlow Electric Manufacturing Company 

CLS200 and MLS300 Cascade Control 

 Setup and Tuning of Cascade Functions 

Tuning Cascade Loops

The proper procedure for tuning cascade control loops is to first tune the secondary (inner) heat or cool control loop 

using all three of the PID modes. This loop must first be tuned to good PID control parameters before doing any 

tuning of the SP temperature control loop. Do not try tuning both loops at the same time unless you are an expert in 

tuning PID loops and have experience with cascade control systems. 

If cooling is in use and there is a proportional component to the cooling control such as using a TP output with a 

solenoid valve, then the PID modes can be tune as well. 

The use of autotuning or adaptive tuning can be used to achieve the PID control parameters. If these tuning 

functions are not available then use manual PID tuning methods. After a satisfactory control is achieved with the 

heat control loop, take note of the P and I values. 

To tune the primary (outer) SP control loop, first check the actual range of the SP of the secondary loop by placing 

the SP loop control into manual mode. With a heat output of 0%, the SP of the heat control loop should be at the low 

SP value as set in the cascade menu. Change the output to 100%, the SP of the heat control loop should be at the 

high SP value as set in the cascade menu. If using cooling control do the same thing with the heat output at 0% and 

then changing the cooling output to achieve the same values as set in the cascade menu. 

Use the values as noted in the PB mode and TI or RM of the Integral/Reset mode of the heat control loop and place 

them in the PID parameters of the heat control output. If PID values are obtained for the cooling, use them for the 

cooling PID parameters. DO NOT USE THE DERIVATIVE MODE. IT MUST BE TURNED OFF. 

Place the control mode of the SP loop into Auto control mode. The SP loop control output should start changing 

which in turn will be changing the SP of the secondary or heat control loop. Allow the process to settle down. If 

there is any unwanted cycling of the temperature, use and change the PID parameters of the SP control loop for 

changing any unwanted control deviations from SP. Do not use the heat control loop for making any changing to the 

PID parameters. 

A slow process will take time to see how the tuning is doing so don’t be in a hurry. A space of 20 to 30 minutes is 

not too long in most cases. 

If you are not knowledgeable or trained and have experience with PID and tuning be sure to see the instructions on 

PID and PID tuning before attempting to tune cascade loops. 

Watlow TRU-TUNE+ can do the tuning for you. First, perform an auto tune of the heat control loop by placing the 

control mode into Tune. After the adaptive mode has been active for a while such as 1 or 2 hours, use the P and I 

values as obtained in the adaptive mode for the P and I values of the SP loop. Place the SP loop directly into 

Adaptive Mode for final tuning of the SP PID values.