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NCS1 Electronics Pack Interface Unit [IFU]

Technical Information

Catalogue No: C1172
Category: Navigation/Inertial
Object Type: Signal Interface
Object Name: NCS1 Electronics Pack Interface Unit [IFU]
Part No: CD11730
Serial No: 90FJB230
Manufacturer: Marconi-Elliott Avionic Systems Ltd
Division: Inertial Navigation [IND]
Platform(s): Naval 
Year of Manufacture: circa 1976
Width (mm):
Height (mm):
Depth (mm):
Weight (g):
Location: Mezzanine Store, NCS Side-Room

Marconi-Elliott Avionics
Interface Unit
N.S.No. 6605-99-529-3908
Drg. No. CD11730
Ser. No. 90FJB230
Wt. (kg) 16
DL. Iss. 7
Marconi-Elliott Avionics
Chassis Assy. I.F.U.
N.S.No. 6605-99-525-8291
Drg. No. CD11655
Ser. No. 89FJB238
Wt. (kg)
D/L Issue 13


This Interface Unit (IFU) is from the Electronic Pack (EP) of the NCS1. The IFU is located at the lower part of the EP between the two Inverters on the left and the Digital Computer Unit (DCU) on its right.

The IFU converts system analogue signals to digital form and buffers them to the Digital Computer Unit [DCU]. It also buffers the DCU digital outputs before converting them into analaogue signals for use in control circuits; it also produces timing, sequencing and alarm signals.

The Naval Compass Stabiliser NCS1 is a stabilised gyrocompass system designed to provide heading and vertical reference data for systems that use such data, on board a ship. Development of NCS1 started in 1971 and quantity production was underway by 1976 with 80 systems delivered to British and other Navies by 1984. NCS1 provides as standard outputs of Heading, Pitch, and Roll but with an additional card can give own ship acceleration and velocity. The ships Latitude and Longitude are continuously computed.

There are three major units; Space Reference Unit (SRU), Electronic Pack (EP) and a Resilient Mount Assembly (RMA).

The SRU comprises a stabilised platform containing 2 two axis gyroscopes and 2 single axis accelerometers mounted in a gimbal system which is contained in a closed binnacle with associated control electronics.  

The RMA is used in frigates and submarines and basically supports the SRU but importantly protects it against vibration from the ship and from shock up to 190g. In addition the RMA transmits the ships acceleration and attitude to the SRU and provides the facility for aligning the SRU with the ship datum planes. In fast Patrol Boats and vessels where any potential shock is likely to be much lighter (typically <15g) a lightweight mount assembly, the LMA, is used.

The EP contains a Digital Computer, Interface Unit, Control /Indicator Panel, Power Inverters and a Standby Battery. The computer is the 12/12P which was a product of the Airborne Computing Division at Rochester (with a part number 59-018-02). The 12/12P was probably the first production version of the 12 series to be introduced, in 1973. It had a 4K, 2 microsecond, core memory and instruction times very similar to those of the Elliott 102C/Minim. The Interface Unit carries out such functions as synchro digital conversion, analogue to digital conversion and the reverse, signal buffering and built-in test. A Control and Indicator panel hosts switches and displays to select the mode of operation, set in information, display selected outputs and enable computer controlled or manual testing.

The Transformer Rectifier units convert ship’s power to 28v dc and in the event of a supply failure the 24V standby battery will support the system for 30minutes. Two identical controlled inverters produce all the regulated dc supplies required by NCS1. The EP has a cooling fan driven by a separate power supply and there is a heater in the base to prevent condensation when the equipment is switched off.

All the items in the NCS1 have a Nato Stock Number inscribed and also have a five digit 'CD' number.

Initial sea trials were carried out in HMS Antrim. NCS1 was designed and manufactured within the Guidance Systems Division at Rochester between 1976 and possibly beyond 1984.

The NCS1 is a tall unit and there is a story that in order to calibrate the system using the Pole Star that a hole had to be cut in the roof of the clean room test area!


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