MR- Sensor Datasheet Page 1 of 8 www.maccon.de

ABSOLUTE ENCODER

for AEROSPACE and Hi-Rel APPLICATIONS

MR-Encoder with reluctance tooth-wheel Nonius-rings

Figure 1. MACCON MR-Encoder Assemblies

CHARACTERSISTICS

The MACCON MR-Encoder has been developed for the measurement of absolute position in extreme

physical environments with a resolution up to 19 Bits. It is especially suited for use in Aircraft and Space

and is undergoing full space-rating qualification to ESA standards.

Summary of the benefits of the MR-encoder:

Fully passive with NO integrated electronics, based on the GMR effect (Giant Magneto-resistance)

Only potentiometers, resolvers and Inductosyn© are comparable

Due to its simplicity and passive structure the MR encoder is highly robust and reliable

Encoder rings can be scaled to fit the application; hollow-shaft designs are easily implemented

Highly flexible with regard to positioning and mounting of reading head(s)

Accurate, light and low power consumption

Measurement is absolute over 360° (temporary position loss is immediately corrected).

Incremental measurement requires one tooth-ring only

Duplication of reading heads allows direct implementation of multiple redundancy

Insensitive to environmental influences, such as magnetic and radiation fields, as well as to

temperature and shock

Very high signal bandwidth (>> 1 MHz), ideal for precise position measurement at high speed,

excellent servo-loop response

Signal conversion is external to the reading head, either integrated in or external to the user’s

controller. An external signal conversion box (to SSI) is available.

MR- Sensor Datasheet Page 2 of 8 www.maccon.de

TYPE DESIGNATION

Currently available types:

S-MR-038-14-37/36C-XXX-RO

S-MR-076-14-75/74C-XXX-RO

S-MR-085-14-84/83C-XXX-RO

Measuring ring:

S-MR-076-14-75/74C-XXX-RO (-RO = ring only)

S = Sensor

MR = (G)MR type

-076 = ring outer diameter in mm (tooth tips)

-14 = ring length in mm (including both N and N-1 tracks)

75 = number of teeth or cycles on N-track

74 = number of teeth or cycles on (N-1)-track

C = cycles

XXX = customer modifications

RO = ring only

Reading head:

S-MR-3.14-XXX-HO (-HO = head only)

S = Sensor

MR = (G)MR type

3.14 = ring pitch in mm (distance between tooth tips)

XXX = customer modifications

HO = head only

TECHNICAL DESCRIPTION

Ring and Head

The data given here is for one encoder ring and one reading head, sufficient to measure absolute position.

Data is given for the encoder ring type: S-MR-076-14-75/74C-XXX-RO

System OD 92mm circle (ring OD + 2 measuring heads + airgap)

Ring outer diameter, OD 76mm (37mm minimum; 85mm maximum)

Ring inner diameter, ID 25mm (can be adapted, see Fig. 2)

Ring thickness (axial) 14mm

Ring mass 115g (depending on hub structure)

Reading head dimensions 32 x 21.5 x 7.5mm, without flat-band cable and connection

box (with flat-band cable see Fig. 2)

Reading head air-gap 0.5mm nominal (0.4 - 0.6mm for signal level adjustment)

Reading head mass <20g

Permissible eccentricity 0.03mm TIR

Cycle length (pitch) 3.142mm

No. of tracks 2 (N and N-1 cycles)

No. of cycles (C) 75 (N) and 74 (N-1)

Resolution >= 18 Bits

Resolution scales linearly with the diameter of the ring

Supply voltage 5Vdc nominal (3.3 to 24Vdc)

Reading head interface sine/cosine analog (8 wire + ground)

MR- Sensor Datasheet Page 3 of 8 www.maccon.de

Signal output 120mV pk/pk. +/-50% (@5V)

Channel symmetry <5% sine/cosine analog

Signal offset <20% of signal output pk./pk. (compensated in converter)

Power requirement <80mW per reading-head (@5V)

Temperature range (storage) - 55 to +125°C

Temperature range (operation) - 40 to +85°C (wider temperature ranges to be verified)

Radiation resistance >100kRad; >10 MRad (to be verified)

Figure 2. Drawings of typical MR-Encoder ring, S-MR-076-14-75/74C-XXX-RO and MR-Reading head, S-MR-3.14P-XXX-HO

Figure 3. Encoder ring and close-up of Reading head

MR- Sensor Datasheet Page 4 of 8 www.maccon.de

SIGNAL CONVERSION ELECTRONICS

TYPE DESIGNATION

S-MR-2-XXX-YYY-SCB

S = Sensor

MR = (G)MR type

2 = dual channel

XXX = SSI, SSI interface; XXX= INC, Incremental encoder

YYY = 030, 300mm cables (open ended); YYY = Customised, t.b.d.

SCB = Signal Conversion Box

DESCRIPTION

The reading head supplies differential, analog Sine and Cosine signals from each signal track (N and N-1),

8 single plus 2 supply lines. The MACCON signal conversion box can process the signals from TWO

redundant reading heads and converts them to serial, digital data (SSI format). The two signal conversion

circuits in the box are fully independent and isolated from each other.

Figure 4. Signal Converter (open, showing configuration interfaces), left Converter with interface box and reading head, right

Features:

Signal conversion electronics with 4 A/D converter channels

Arc Sin/Cos and Nonius conversion in GC-NIP chip

Serial digital output (SSI)

2 independent channels in one box, for redundant reading heads

Connector

Dimensions:

Dimensions: 40 x 30 x 30 mm

Mass (without connection box and cables): 180g

Connector, controller side ITT Cannon MDM-15PH003M2-A174 (15 pin)

Cable, sensor side; two cables 200mm long (or specify)

The reading head is fitted with a short flat-band cable and contact interface PCB. As a customized option

MACCON can supply reading head(s) directly attached to interface boxes (60g) and the signal conversion

electronics (see Fig. 1 and 4).

MR- Sensor Datasheet Page 5 of 8 www.maccon.de

Figure 5. Internal circuit of Signal conversion electronics (one channel)

Figure 6. Drawing of Conversion Electronics Box (one side open)

TECHOLOGY & MODE of OPERATION

This encoder operates by exploiting the change of magnetic field, when the air-gap between a small

permanent magnet and a ring, having a cyclic sine-wave profile (salient teeth are distributed around the ring

with a constant pitch length) and being of ferromagnetic material, caused by rotation of the ring. The field

change is detected by a minute GMR resistive sensor film (GMR = Giant Magneto-resistance effect).

The sensor consists of two Wheatstone bridges, each made up of 4 GMR resistors, offset by a ¼ tooth

pitch, which experience Sine and Cosine resistance variations due to the changing magnetic field (See Fig.

7). These resistance variations are detected by observing the voltage difference between the center-taps of

two arms of the Wheatstone bridges; both are covered with a bias permanent magnet and fed with a

common voltage. This configuration automatically suppresses common-mode interference and the influence

of supply voltage changes.

MR- Sensor Datasheet Page 6 of 8 www.maccon.de

Figure 7. Two offset GMR resistance bridges in one sensor (2 sensors per reading head) The internal structure of one GMR resistor

The sensor itself just provides analogue voltage outputs (one sine and one cosine channel per track).

Figure 8. Two Wheatstone bridges for one sensor (each track)

Two sensors are integrated in one reading head; these observe the two tooth tracks of the ring, which ar e

separated by 8mm. Signal processing is necessary to compute the absolute angular position.

The two tracks are needed to allow absolute position to be detected over 360° (via N/N-1 Vernier principle –

see: http://en.wikipedia.org/wiki/Vernier_scale). The two adjacent reluctance patterns deliver a different

number of electrical cycles (N and N-1). The single cycle offset per revolution delivers uniquely different pitch

position values from the two tracks within every cycle during 360° rotation of the ring.

Figure 9. Illustration of Nonius Principle (N, N-1)

MR- Sensor Datasheet Page 7 of 8 www.maccon.de

In total, two magnets and 4 GMR sensors (each consisting of 4 individual GMR resistor elements, wired as

a Wheatstone bridge) are incorporated in one reading head. Two or more identical but physically and

functionally independent sensor heads can be used for redundancy purposes.

REFERENCES: MR-TECHNOLOGY in SPACE

“Spirit” and “Opportunity” Space rovers (Maxon Motor) – in mission

MERTIS on Bepi Colombo (Kayser Threde; OHB) – fully qualified

MACCON has further experience in space-rated sensors from the programs: Meteosat scanner

(Eumetsat), LCT on TeraSAR, GEO et al., MHS on FY3.

Curiosity” (Aeroflex/NASA) – in mission: Over 20 MR position sensors are used on this space

vehicle.

Figure 10. CURIOSITY Mars Rover; See: https://www.nasa.gov/mission_pages/msl/index.html

The same MR technology has proven itself in mass applications, such as automotive, mining, industry and

transport. One example of such a product can be found at https://www.lenord.com/products/minicoder/gel-

2449/ (in this case electronics are integrated in the measuring head). With the support of our development

partners we have improved many aspects of this design to meet the materials and reliability demands of the

aerospace industry.

Disclaimer: due to ongoing qualification technical details in this datasheet still subject to change.

Our MR-technology partners:

MR- Sensor Datasheet Page 8 of 8 www.maccon.de

Main tests of sensor system (incl. sensor heads and converting electronics as in Fig. 4) during

screening:

Bake-out:

o 72h @ +85(+5)°C and 10-6 mbar

Electrical tests:

o Isolation test and component tests

Functional Tests

o Analogue signal measurements or position accuracy measurements with nonius

measurements at different temperatures

Visual Inspections

Burn-in:

o +85 (+5) °C for 240h.

Optional tests performed during qualification:

Shock tests

Vibration tests

Thermal cycling (thermal shock)

Thermal Vacuum Electrical Performance Test

Life test at +85 (+5) °C for 2000 h

Radiation tests

Outgassing test according to ECSS-Q-ST-70-02C

Destructive physical analysis - microsectioning