Archive for category Temperature
As energy costs and environmental concerns continue to rise, we count on our facility managers to take control of building/factory energy consumption. To reduce their companies’ carbon footprints, facility managers have begun implementing energy management programs to control their systems, optimize efficiency, and manage expenses.
But how are they doing it?
Let’s say you are trying to cool your facility. There are two steps to determining how much energy is consumed in the process. Read the rest of this entry »
RTDs are great temperature sensors – accurate and easy to install. But they are not friendly when it comes to trying to get a single RTD to go to two places, like when an RTD temperature measurement has to go to both a controller and a recorder. People call and ask, “How do I split an RTD signal?” The short answer is, “You can’t.”
An RTD cannot be wired in parallel or in series to a second device. Any RTD input supplies a known, regulated ‘excitation’ current to the RTD. Mixing RTD inputs would mix currents and that’s a Big No-No.
There’s also a lead wire compensation circuit for 3- or 4-wire RTDs that would create problems if a single RTD were connected to two different RTD inputs. There’s just no feasible means of making two RTD analog inputs play nice together.
But all is not lost. There are several ways to achieve your goal.
One thing I’ve learned in this industry: Even though there are standards to thermocouple color codes and types, the most basic rule for installation (In the US, when you’re wiring a thermocouple, RED is always negative) is non-intuitive to anybody who’s ever done electrical wiring.
It’s pretty easy to tell when you’ve done it wrong: You wire the thermocouple directly into an instrument, and as the process gets hotter, readings say it’s cooling down. As your process cools down, the readings show a rise in temperatures. If you reverse the wiring at a junction box, it’ll read in the right direction, but you’ll have errors because of the false junctions.
Here are some basic wiring diagrams from the reference section of the Lesman catalog, with rules to follow, and some suggestions on specifying the right thermocouple wire.
If you use thermocouples in high-temperature applications, you’re aware of the issues thermocouple drift can cause. Thermocouples drift. It’s not a question of IF, it’s a question of WHEN. And thermocouple drift costs processors time and money in processing errors, waste, downtime, and lost production.
Thermocouple drift occurs due to metallurgical changes of the metal alloy elements over the extended use of the sensor. Thermocouples can drift by as much as several degrees per year.
The following is an excerpt from “Digital switches with self-diagnostics can improve results and ease the implementation of safety systems” by Rick Frauton of United Electric, originally published in the September 2011 issue Pumps & Systems magazine. Rick is the product manager for UE’s One Series line of electronic pressure and temperature switches, and has been working with customers to identify applications where these switches can improve application and plant safety. Thanks, Rick, for being our guest blogger this week.
Years ago, most switches were blind mechanical devices actuated electromechanically or by pneumatics. They offered no indication of reliability, such as success or failure in response to a command. This lack of feedback was particularly worrisome in safety applications. The result could be catastrophic, should a malfunction occur in place of the proper response to a tripped pressure or temperature alarm.
Industry surveys say that nearly half of all processes aren’t accurately tuned. If you read my post on accuracy, stability, and repeatability, you’ll know that a poorly tuned process can result in bad readings, downtime, and wasted materials.
If you use a Honeywell UDC2500, UDC3200, or UDC3500 1/4 DIN universal digital controller, there’s a great built-in function called Accutune that can help make sure your control process is properly tuned.