United Electric Controls has added two DC-voltage switching models to its One Series Safety Transmitter (ST) line. With its ability to directly switch 24 VDC and 125 VDC as well as 250 VAC loads, the One Series ST models can now provide SIL 2-certified control for many types of final elements including pilot valves, actuators, motor controllers and other SIS elements, without involving a DCS or safety PLC.
"Many control schemes are transitioning to low-voltage equipment, primarily to reduce electric shock hazards in the plant or are looking to improve response time and reduce costs by switching final elements directly from the transmitter. By enabling switching of 24 VDC and 125 VDC final elements from our safety transmitters, we've made it possible for more companies to add simple and cost-effective SIL 2 safety loops in the field where a PLC or DCS may not be available," said Wil Chin, Vice President of Marketing and Business Development, United Electric Controls, adding that the ability to directly control legacy equipment that utilizes 125 VDC control schemes is especially valuable to power plants.
One Series safety transmitters reduce cost and improve safety by embedding a process sensor, logic solver and safety relay in a single, SIL 2-certified field device. Although it looks like a traditional temperature or pressure transmitter, the ST can also switch final elements such as valves, motors, and blowers directly from the transmitter, maximizing response time while eliminating the wiring inherent in having to route a shutdown or alarm response through a PLC or another safety controller.
To address the growing demand for lower voltage switching of 24 VDC equipment, United Electric Controls has now added a Safety Relay Output (SRO) capable of handling 0-30 VDC at 6 amperes. To meet the needs of customers who were using 125 V DC equipment, most of whom are in the power industry, UE has added an SRO capable of switching 0-130 VDC at 2.5 amperes. With these additions, One Series Safety Transmitters models can now be specified for either pressure or temperature monitoring at any of the following current levels:
- 12-250 VAC @ 5 mA-5 A (Model 2SLP47)
- 0-30 VDC @ 6 A, 1.8 A Pilot Duty (Model 2SLP48)
- 0-130 VDC @ 2.5 A, Q1501 Pilot Duty (Model 2SLP49)
All One Series Safety Transmitters provide 4-20 mA NAMUR NE 43 standard output with exclusive "I Am Working" diagnostics. The transmitters are certified for use in SIL 2 safety instrumented systems, and are capable of SIL 3, per IEC 61508. They have configurable self-diagnostics and achieve a safe failure fraction of 98.8%. Additional low-level discrete outputs communicate health and set point status, ideal for voting logic schemes. Instrument response time is <100 milliseconds.