Plant Safety, Safety Relays on Transmitters, Transmitters

The One Series Safety Transmitter: Safety You Can Rely On

When it comes to plant safety, SIS designers want simplicity, versatility, and the very best equipment available. We believe that in this way our One Series Safety Transmitter provides all that. Its unique design gives the extra peace of mind that the product will perform its intended function when required, providing for greater safety and reliability at all times.

What makes the One Series Safety Transmitter so one-of-a-kind? One way is through the use of discrete outputs, a rather unique feature in a safety transmitter. In addition to the 4-20 mA analog output, discrete outputs provide another way to remotely monitor the health status and set point status using a logic solver, facilitating voting logic SIS designs. A programmable safety relay output (SRO) is also included, capable of switching a high voltage/high current load directly. When connected to the final element, the need for a separate logic solver is eliminated.

Why is voting logic so important? People in this industry of course want the plant to be safe, but are also concerned with the nuisance trip factor. A safety system in its simplest form includes one transmitter, one logic solver, and one final element—this is called a simplex system. What this means is that if the transmitter decides the pressure is too high, the decision to alarm is up to that transmitter alone. In the event of a failure, there is no backup; you are relying on that instrument to make the right decision.

This is often countered by using two transmitters, known as a redundancy system, requiring both transmitters to be in agreement before an alarm is sounded.

This is where our One Series Safety Transmitter is truly unique. By providing discrete status outputs and the SRO from the transmitter, plus a 4-20 mA NAMUR standard output, the SIS designer has more versatility on how the system will react to a process upset. Our exclusive I Am Working™ output, which is the self-diagnostic status of the product, is normally closed and indicates that everything is working properly in the transmitter. With this extra assurance, it is possible to eliminate the need for a second transmitter.

The Safety Output Relay (SRO) status will remain closed when not at the set point, and opens when the set point is reached.

For example, if the pressure is trending upwards but hasn’t reached the set point yet, and the I Am Working ™ output is still closed, you have assurance that the Safety Transmitter is indeed working. The decision may be to sound an alarm only, rather than shutting down the plant unnecessarily. The One Series Safety Transmitter provides the ability to distinguish between alarm and shutdown conditions to avoid nuisance trips.

We understand that in the end, the most important thing is safety. United Electric Controls’ safety, alarm, and shutdown expertise has allowed us to provide the most versatile Safety Transmitter certified for use in SIL 2 applications and is capable of SIL 3 with redundancy.