In a setpoint programmer you can set up a profile in the controller in which the setpoint varies in a pre-determined way over a period of time. Temperature is a very common application where it is required to ‘ramp’ the process value from one level to another over a set period of time.

A single profile can be set in controllers such as the 2416, 2408, 2404, while the 2604 and 2704 controllers will program up to three separate profiles (these may be temperature, pressure, light level, humidity, etc., depending on the application).

The Program is divided into a flexible number of Segments - each being a single time duration, - and containing details for each profiled setpoint. The 2400 series can store up to 16 separate program each of 16 segments, while the 2604 has a capacity of 50 programs of up to 100 segments each (500 segments total), and the 2704 can hold up to 60 programs of up to 100 segments each (600 segments total).

In addition to controlling the setpoint during each segment of the profile, the controllers can also activate DIGITAL EVENTS during a segment. The 2400 series can activate 8 separate digital output flags, while the 2604 and 2704 can activate up to 16. In addition to these segment digital flags the controllers can provide outputs for END of program or which program is running.

Once a program is completed, it can be set to end repeat any number of times, or repeat continuously.

Holdback freezes the program if the process value does not track the setpoint by an amount which can be set by the user. This feature ensures that during a process such as heat treatment of metals, the product is guaranteed to have held at the required temperature for the required time.

In a RAMP it indicates that the process value is lagging the setpoint by more than a settable amount and that the program is waiting for the process to catch up.

In a DWELL it will freeze the dwell time if the difference between SP and PV exceeds settable limits. In both cases it guarantees the correct soak period for the product.

Holdback can be defined to activate when the PV is below the SP by a pre-set value or when the PV is above the SP by a pre-set value.

Holdback Example: Holdback, operating in each segment, is often used in a temperature control application as detailed below:- During a ramp up period the holdback type may be set to deviation low. If the Process Value lags the programmed rate of rise, holdback will stop the program until the PV catches up. This prevents the set program from entering the next segment until the PV has attained the correct temperature.

During a dwell period the holdback type may be set to deviation band. This guarantees that the dwell or soak period operates only when the process value is within both high and low deviation limits. During a ramp down period the holdback type may be set to deviation high. If the process cannot cool at the rate set by the ramp down rate the program will be held until the process catches up.