How to Reduce Scrap with the Watlow Aspyre: Open Heater Detection

One of the best ways to decrease your operating expenses is to reduce your scrap. In this video we're going to talk about process heating and controls and specifically Watlow's new power controller called the Aspyre.

The Aspyre is Watlow's latest innovation in power control theory and it has a variety of features that are going to help guide this conversation. But today we're going to focus on one called the open heater detection.

So let's set the stage...your company has a process that includes a heat cycle like the curing oven. Parts are gonna flow through this oven at a regular rate producing a certain number of parts per hour with a certain percentage of nominal scrap.

It's a standard thermal have a bank of heaters and those heaters are being controlled by a power controller, which is in turn controlled by a temperature controller. And you have a thermocouple or RTD in the system in the oven somewhere. For simplicity's sake let's say it's nine elements wired in three-phase Delta and it's all one circuit.  Let's say you're in the middle of production run and bam you lose an element. This is going to do three things; it's going to increase the resistance to the remaining elements, it's going to create a slightly unbalanced electrical load and it's going change the thermal dynamic properties inside your oven.

Now keep in mind in a standard thermal loop your sensor, unless it's located in exactly the right place, probably isn't gonna even know so you don't have any alarms or indication that you've lost an element. Now let's say you lose another one. Now seven elements are doing the work of nine. This is going to significantly change the temperature profile inside your oven and although it may not be obvious at this time, it's going to increase your scrap rate. By now the sensor has noticed that there's a deficiency of heat and it's calling for a hundred percent output through the temperature controller to the elements. But because seven elements are doing the work of nine they're already at full power and there's no additional capacity to give.

This situation can exist for a long time where your product is continuing to flow through the product itself isn't getting enough heat and it was producing say undercooked widgets and your scrap rate downstream is rising significantly.

Let's take that same scenario now and rerun it replacing the standard power controller with a Watlow Aspyre. The Aspyre has the
ability to sense an open heating element on a resistive thermal circuit by means of an integrated current transformer. Now the load of an electrical circuit is going to be measured in amps and amps as a function of resistance and voltage but when one of those heating elements pops it changes the resistance which changes the amps. The Aspyre SCR then looks at that change evaluates it and alarms out to an operator and says hey you've got a temperature element that's down. In addition, remember in our previous example where unless that sensor was located in just the right spot, it couldn't even tell if the heating element had failed. You would need to have two or three elements fail before the sensor would figure it out send a signal to the temp controller and then the temp controller would come down and in turn tell the power controller towork a little bit harder.

Well because the Aspyre is on the power side of the equation, it senses immediately when one of those elements pops and it's able to take action. It reroutes the remaining power to the other elements thus ensuring a consistent even heating profile in your oven. All of this is designed to reduce scrap and increase efficiency.