With the expense of replacing failed obsolete meters rising year by year, a standardised universal alternative can both reduce user error and curb costs


DB40 replaced 100% Form, Fit, and Function by Otek's PNP

FAILED ANALOG OR DIGITAL METERS in nuclear control rooms require replacement by seismically-qualified, safety related equivalents. The cost of replacement equipment rises higher the farther past the obsolescence date of the device.

Modern Class 1E LED meters like the PNP (Plug N Play) and NTM (New Technology Meters) allow for better Human System Interfaces (HSI) while providing easier replacement methods.

New meters are modular that separate I/O, display, mounting, and signal conditioning. Using a “true white LED” display allows for in situ printed overlays to be installed on front scale plate of the “one movement” display. These can accommodate any colour, scale or text with defined colour transitions based on the application.

Standard mounting adapter plates (if necessary) fit the present mounting holes and space of the old meter in the control board. A generic hub secures to the back of the display unit. A universal I/O board fits within the hub, which can be configured to accept the field signal and power (if required).

As an alternative, the I/O board could be installed in the housing of the meter. The replacement uses standard housing and an I/O board that can be configured for the input signal. The remaining parameters to be selected are the display, face plate and adapter plate (if needed). Form, fit, and function (FF&F) will be the same as the replaced meter.

Developing a general installation specification allows replacement as old devices fail or as dedicated replacement campaign. The additional benefit of these FF&F replacements is that they are available for the following applications:

  • 1) display only
  • 2) displays powered by the signals they measure (like analogs) with controlling outputs such as relays
  • 3) solid state relays with fail safe contacts
  • 4) 4-20 mA current loop transmission,
  • 5) retransmission
  • 6) PID options


Replacements with only solid state components like the PNP will avoid lengthy cyber security evaluations, while NTM allows more customisation and external serial communications and control.

The signal conversion can be moved to distribution panel/cabinet with a 4-20 mA Current Loop transmitter that uses the identical circuit in the PNP HUB is available in three packages: DIN rail, panel mount and explosion proof.

The transmitter includes two displays that monitor the input and output signals simultaneously, accepts same input signals, and power plug in modules than the PNP. The transmitters allow signals to be standardised to 4-20 mA and use loop powered meters. This makes the meters on the control board a simple replacement with correct faceplates.

If the existing signal wiring from the distribution panel/cabinet to individual meters qualifies it can be used to carry the current loop signal/power to existing meters eliminating the need for rewiring.

The benefit of using the transmitter would be having one standard display type for meter replacement for all applications.

For more information, please contact Dr Otto Fest, OTEK Corporation, opfest@otekcorp.com and mention Nuclear Engineering International when responding