General Purpose Logic Circuit Device Spotlight

September 4, 2018
Tech Tuesday

Most of Functional Devices, Inc. products are designed for general-purpose use. Our enclosed relay products, for instance, are rated to control many types of loads, and they can be a great fit in almost any control scenario. Some of our products were conceived for a specific application, but their use in other applications is limited only by the imagination of the user (and the device’s ratings, of course). Models RIBMNLB-6/-4/-2 are a great example of this design philosophy.


These products were designed for AHU Fan Safety and Alarming purposes, but they are also known as Logic Boards; that’s where the LB in the model name comes from. The function of the product is simple, and they can serve as a monitor/control device for many applications. While the products specifically highlighted here are meant to be panel mounted, we offer the -6, -4 and -2 models in an enclosed version also (RIBLB-6/-4/-2).


Each of the above devices have a Master relay on them, which is controlled by the device’s 2, 4 or 6 inputs. If all the inputs are Closed (typically a Normally Closed sensor), and the device has power, the Master relay will be energized. If any of the inputs Open, the Master relay is de-energized. In a fan safety application, the inputs would typically be wired to Low Limit, Static Pressure, Smoke Detector and other associated sensors. If any of the inputs go into alarm, the RIBMNLB would handle shutting the fan down until the fault was corrected.

There are on-board LEDs to indicate device power, status of each input and Master relay status. Each input is also provided with a local override switch that will allow it to be bypassed; this prevents the need to insert a jumper wire to simulate a Closed input. There is also a dry contact output associated with each of the 2, 4 or 6 inputs, and they follow the state of the input. These outputs can be connected to a controller for purposes of monitoring the inputs and determining the cause of a shutdown. The Master relay has two 24 Vac powered outputs and one dry-contact output that is rated for up to 10 Amps @ 277 Vac.

As a general-purpose device, the possibilities for use are endless. If you have used one of our logic boards in an obscure application, let us know, and maybe we can feature the application in a future blog. We love to hear about our products being used in unique and niche applications.

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About the Author

Henry Smith is a 34-year-old engineer at Functional Devices, Inc. He has a BS EET obtained from Purdue University in 2014 and a lifelong interest in electronics. As an engineer at Functional Devices, he gets to provide Technical Support to our customers, from distributors to specifying engineers and installers.

Henry enjoys providing tech support, as it allows our company to assist at every level of our product’s lifecycle and exposes us to interesting and unique applications. While not every technical question is unique, even answering a simple question or providing someone with the information in a timely manner can go a long way to helping him or her meet a deadline.