Over the years we have had the opportunity to work with many individuals and companies on a variety of process controls issues and challenges. Here in no particular order are some "tips and tricks" for process controls
Actuators come in many flavors and configurations. Wiring these can range from easy to challenging. For such a simple straighforward machine, it seems to confound many who attempt to replace or install these items. Eurotherm controls have a remarkably simple solution for driving actuators. Simply put, these controls use the transit time to determine the position and output requirement for accurate control. In most cases, this does away with all the slidewire and related wiring complexity. And a new controller such as 2208 is often less expensive and provides far better accuracy than utilizing a converter between the actuator and old controller!
A flashing Sbr error code strikes fear in all but the bravest technician. It always happens when you have a job to finish or a deadline that everyone's nervous about. If you're lucky, you have a spare sensor (you did know that Sbr code stands for sensor break -- broken thermocouple -- didn't you?) But if not, you may still be able to continue. Take the dead thermocouple, strip or clip the end, and twist the ends together. Pick a spot near where the old thermocouple mounted and get creative. Friction fit, sheet metal screw, clamp wrench, even a radiator hose clamp. If you're lucky, you'll have a temperature indication again and can continue until you get a "real" sensor to replace the temporary.
My tuning is slow, overshoots, varies up and down around setpoint. Controller tuning is the most misunderstood aspect of temperature control. Eurotherm has done an excellent job establishing a universal tuning system that covers most applications. But default tuning always starts with safety. And in most cases, safety means slow. And unfortunately the slower your process reacts, the harder it is to control. If its really really slow, you may have to defeat the tuning altogether and use the controller as a simple on off device. But in most cases, tuning adjustment will result in better and faster control. So....you did auto tune....right? The most common mistake in autotuning is doing so at a setting you don't normally operate at. So here's an easy tip. Always tune at 80% of your normal sepoint. You run at 700 degrees F, fine, tune at 575. Oh and you did put a "load" on your application, right? Put a couple of bricks in your oven before you tune. You'll be glad you did.
Eurotherm controls have AC instrument wiring legends of L and N to show the correct position of power wiring to operate the instrument. They also have V+ and V- to show the correct position of input wiring. Like to guess how often we get calls about Sbr errors on new installations? If you're very lucky and accidently reverse the wiring and catch it fast enough you may survive such a mishap. But if not, well.....do try to follow the wiring legend. You'll be glad you did.
Ah the wonderful delight of SSR devices. These wonderful "hockey puck" devices have greatly reduced the wiring challenges of heaters and other AC devices over the years. With the bad (and somewhat unfair) rap that mercury contactors have gained, more and more controls are moving toward SSR devices. Do you know the biggest drawback to these? Thats right....heat.... And guess what it does in Texas? Yep....gets hot. Want better life for these fabulous devices? Mount on the biggest heat sink you can and be sure the sinks have air movement....cooler air movement. Won't help to have a heat sink the size of a toolbox if the air movement is zero or just hot air inside a panel blowing around. Oh and you do know that the hotter it gets, the less load these can switch, right? Cooling air....thats what these devices need.