Product Information

ERA 7900 Series
ERA 8900 Series
Scale-Tape Angle Encoders
with Very Large
Operating Tolerances

12/2023

Reliability

Exposed angle encoders without integral
bearing from HEIDENHAIN are optimized
for use on fast, precise machines. In spiteof the exposed mechanical design, they
are highly tolerant to contamination, ensurehigh long-term stability, and are quickly andeasily mounted.
Lower sensitivity to contamination
Both the high quality of the grating and thescanning method are responsible for theaccuracy and reliability of the encoders.
Encoders from HEIDENHAIN operate withsingle-field scanning. Only one scanningfield is used to generate the scanningsignals. Local contamination on themeasuring standard (e.g. fingerprints or oilaccumulation) influences the light intensityof the signal components, and therefore of
the scanning signals, in equal measure. The
output signals do change in their amplitude,
but not in their offset and phase position.
They remain highly interpolable, and theposition error within one signal period
remains small.

Linear scaleWindowsStructured
detector

Semitransparent layer
Transparent layer

In the DIADUR process, hard chrome
structures are applied to a glass or steel
carrier.
Scanning reticle
Condenser lensIndex grating

LED light source

Photoelectric scanning in accordance with the imaging principle with a steel scaleand single-field scanning

The large scanning field additionallyreduces sensitivity to contamination. In
many cases this can prevent encoder
failure. Even if the contamination fromprinter’s ink, PCB dust, water or oil is up to3 mm in diameter, the encoders continue
to provide high-quality signals. The position
errors within one revolution remain far
below the specified accuracy.

2

Durable measuring standards
By the nature of their exposed design, themeasuring standards of angle encoders
without integral bearing are less protectedfrom their environment. HEIDENHAIN
therefore always uses tough gratings
manufactured in special processes.

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

In the METALLUR process a reflective goldlayer is covered with a thin layer of glass.
On this layer are lines of chromium only
several nanometers thick, which aresemitransparent and act as absorbers.
Measuring standards with METALLUR
graduations have proven to be particularlyrobust and insensitive to contamination
because the low height of the structure
leaves practically no surface for dust, dirt orwater particles to accumulate.

Reflective primary layer

Composition of a METALLUR graduation

Due to the high surface hardness, evenfrequent cleaning will not harm thegraduation.

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

3

Application-oriented operatingtolerances
The operating tolerances of the ERA 7900
and ERA 8900 series have only a slightinfluence on the output signals. Inparticular, a variation in the scanning gap
between the graduation carrier andscanning head causes only negligible
change in the signal amplitude, and barely
affect the position error within one signal
period. This feature permits extraordinarily
large mechanical operating tolerances.

Signal amplitude with and without
signal stabilization in VPP

Mechanical design types and mounting
ERA 7900 and ERA 8900 series

Operating tolerancewith signal stabilization

Nominal scanning distancewithout signal stabilization

Scanning distance in mm
Influence of the scanning gap on the signal amplitude for ERA 7900 andERA 8900

Incremental andReference mark track

Incremental track

Y±0.5 mm

±1 mm

Z±1.2 mm+1.2 mm/-2.0 mm

Roll (X)±2.0 mrad±5.0 mrad

Pitch(Y)±0.5 mrad±5.0 mrad

Yaw (Z)±0.2 mrad±5.0 mrad

The ERA 7900 C and ERA 8900 C angle
encoders are designed for full-circle
applications. Thus, they are particularly
suited to hollow shafts with large inside
diameters and to applications requiring
accurate measurement over a large
circumference, such as large rotary tables
or telescopes.
In applications where there is no full circle,
or measurement is not required over 360°,
circle segments are available for theERA 8900 series.

Mounting the scale tape for full-circle
applications
ERA 74x0 C: An internal slot with aspecified diameter is required for receiving
the scale tape. The scale tape is inserted
starting at the butt joint and is clicked into
the slot. The length is cut so that the tapeis held in place by its own force. To makesure that the scale does not move within
the slot, and that the tape tension is equalover the entire circumference, the tape isadditionally bonded to the slot floor.
ERA 89x0 C: The scale tape is suppliedwith the halves of the tensioning cleat
already mounted on the tape ends. An
external slot is necessary for mounting.
A recess must also be provided for thetensioning cleat. After the scale tape has
been inserted, it is fastened aligned along
the slot edge and tensioned using thetensioning cleat.

The scale tape ends are manufactured soexactly that only minor signal-form
deviations can occur in the area of the butt
joint. Depending on individual conditions(temperature, diameter, thermal expansion
coefficient), various measures are required
to make sure that the scale does not move
within the slot.

Mounting the scale tape for circle
segments

Operating tolerance (in combination)
Axis

The ERA 7900 and ERA 8900 series ofangle encoders consist of a scanning unit
and a one-piece steel scale tape. The steel
scale tape is available up to a length ofapprox.180 m.
The tape is mounted on• the inner ring (ERA 7900 series)• the outer ring (ERA 8900 series)

ERA 89x1 C: The scale tape is suppliedwith premounted end pieces. An external
slot with recesses for the bearing pieces
is required for placing the scale tape. The
end pieces are fitted with tension springs,
which create an optimal bearing preload forincreasing the accuracy of the scale tape,and evenly distribute the expansion overthe entire length of the scale tape.

Operating tolerances for ERA 7900 and ERA 8900 after ideal mounting at
diameters above approx. 3 m

Protection against ambient lightinfluences
Due to the large scanning gap, intensive
ambient light can have a negative effect on
the signal quality of the measuring device.
In these cases, a suitable cover has to beprovided in order to avoid direct illuminationof the scanning head.

Spring

ERA 89x2 C: An external slot or one-sided
axial stop is recommended for placing thescale tape. The scale tape is supplied
without tensioning elements. It must be
preloaded with a spring balance, andsecured using the two oblong holes.

Mounting the scanning head
The provided mounting aid facilitates thecorrect alignment of the scanning headrelative to the tape during assembly.

Cover to prevent the penetration of ambient light into the scanning gap

4

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

5ERA 7900 series
Incremental angle encoders for high accuracy and very large operating tolerances• Steel scale tape for internal mounting• Full-circle versions, also for very large diameters• Consisting of a scanning head and scale tape

ERA 7980 full-circle version

Scanning head

AK ERA 7980

Scanning gap

Nominal 3 mm
Variation ±1.2 mm

Interface» 1 VPP

Cutoff frequency –3 dB≥ 350 kHzElectrical connection

Cable 3 m, with M23 coupling (12-pin)

Cable length≤ 150 m (with HEIDENHAIN cable)

Voltage supply

5 V DC ±0.25 V

Current requirement< 100 mA (without load)

Vibration 55 to 2000 Hz
Shock 6 ms2≤ 200 m/s (EN 60068-2-6)≤ 1000 m/s2 (EN 60068-2-27)

Operating temperature–10 °C to 50 °C

Protection EN 60529

IP40Weight≈ 20 g (without cable)

Scale TapeMSB ERA 7900 C full-circle version

Measuring standard
Grating period
Coefficient of expansion

Steel scale-tape with METALLUR graduation
40 µm
therm ≈ 10.5 · 10–6 K–1

Signal periods

Upon request

Accuracy of thegraduation

According to individual error budget calculation

Reference marksDistance-coded

Scale-slot
diameter

6

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

Full circle 3000 mm to 8000 mm; upon request

Mech. permissible speed

Depending on diameter

Permissible expansion
coefficient of shaft

–6 –1
–6 –1
therm≈ 9 · 10 K to 12 · 10 K
Defines scale slot-floor diameter and tape tension

Protection EN 60529
for entire encoder

IP00

Weight≈ 30 g/m

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

7

ERA 7900 series

ISO 4762-8.8
M3x25



3



*** 4.9 ± 0.1 *** 0.9 ± 0.1

A-ARz 10


0.3 ± 0.01





7.5

15.6

A

0.3 ± 0.01

7.5

0.03
*LE A



A-A

4.9 ± 0.1 ***

B-B
A-A

40

1117



11



B

40.457x45°



°



45





B-B

36°

45

0.1/50 B LE **B

Mounting option i shown

13.2 +0.1
0> 57.5 14



CA-A
10:1
0.5

1513DRz 168




C

2.4 F
1/5000 LE
0.1/500 LE
0.01/25 LE
0.04 LE F
0.01

Rzmax 10



30°

0.6

0.4 +0.15–0.05

, ,  = Mounting options
 = Actual guideway30 = Required mating dimensions
C-C
1 = Scale-tape slot floor  D
2 = Mounting clearance
3 = Positive direction of rotation for output signals as per interface description
4 = Reference mark
5 = Scale-tape thickness
6 = Distance between scale-tape slot floor and thread for fastening screw
7 = Distance between scale-tape slot floor and scanning head’s rear mounting surface
8 = Eccentric bushing (Moiré setting)
9 = Hole required for fine adjustment
10 = Chamfer for accessibility for Moiré setting (mounting option: )
11 = Permissible axial motion (scale tape relative to the scanning head) ≤ ±0.5 mm
12 = Mounting aid for mounting at nominal scanning distance = 3 mm
13 = Mounting clearance (spacer shim)
14 = Installation room for mounting aid
15 = Direction for removing the mounting aid (with mounting option i)
16 = Cover against extraneous light
17 = Notch for scale-tape disassembly (b = 3 mm)*		 = Averaged relative to the total deviation of the scale-tape slot in direction Rx or Ry over 360°**		 = The fine adjustment of the incremental signals and reference mark is performed with the aid of theH8 eccentric bushing*** = The mounting of the scanning head in the Y direction must be performed in the range of the average
deviation of the scale-tape slot in the Y direction over 360°

Rz 16

0.6

121 F
1/5000 F
0.1/500 F
0.025/25 F

0.4+0.15
–0.05

> 16

0.8 ± 0.1

14

 D + (Dx0,00005)

10 6 (2x)

14

13.4

2.8





D-D

11.5

2.5

110.1/50 B LE **
 3.7



M3x5

*LE C

ISO 7092-3-200HV-A2

18.3

ISO 4762-8.8
M3x25



ISO 4762-8.8-M3x(a+5)

+0.5
1 0

19

155.80.03*LE A

M3 (2x)
0.2 A



2.75

30.5



15.6

46

M3 (2x) 0.2 AARz 10aRz 10



-0.05
-0.02

16



YRy+0.2

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

Rx
1.2 ± 0.3

1.2 ± 0.3
17X
Z
Rz

D

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

9

ERA 8900 series
Incremental angle encoders for high accuracy and very large operating tolerances• Steel scale tape for external mounting• Full-circle and segment versions, also for very large diameters• Consisting of a scanning head and scale tape

ERA 8980 full-circle version

ERA 8981 segment version,scale tape secured with tensioning elements

Scanning head

AK ERA 8980

Scanning gap

Nominal 3 mm
Variation ±1.2 mm

Interface» 1 VPP

Cutoff frequency –3 dB≥ 350 kHzElectrical connection

Cable 3 m, with M23 coupling (12-pin)

Cable length≤ 150 m (with HEIDENHAIN cable)

Voltage supply

5 V DC ±0.25 V

Current requirement< 100 mA (without load)

Vibration 55 to 2000 Hz
Shock 6 ms

≤ 200 m/s2 (EN 60068-2-6)≤ 1000 m/s2 (EN 60068-2-27)

Operating temperature–10 °C to 50 °C

Protection EN 60529

IP40Weight≈ 20 g (without cable)

Scale TapeMSB ERA 8900 C full-circle version
MSB ERA 8901 C segment version with tensioning elements
MSB ERA 8902 C segment version without tensioning elements

Measuring standard
Grating period
Coefficient of expansion

Steel scale-tape with METALLUR graduation
40 µm
therm ≈ 10.5 · 10–6 K–1

Signal periods

Upon request

Accuracy of thegraduation

According to individual error budget calculation

Reference marks

Distance-coded

Scale-slotdiameter

ERA 8982 segment version,scale tape without tensioning elements

10Product Information ERA 7900 Series, ERA 8900 Series   12/2023

Full circle ≥ 3000 mm; upon request
Segment ≥ 3000 mm; upon request

Mech. permissible speed

Depending on diameter

Permissible expansion
coefficient of shaft

–6 –1
–6 –1
therm≈ 9 · 10 K to 12 · 10 K
Defines scale slot-floor diameter and tape tension

Protection EN 60529
for entire encoder

IP00

Weight≈ 30 g/m

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

11ERA 8900 series

45°

45°

 3.8 3.8

ERA 89x0 scale tape (full circle)

ERA 89x1 scale tape (segment)

Mounting aid for installation with a scanning gap of 3 mm
(mounting option Ô is shown)

Ô, Õ,  = Mounting options
A = Bearingk = Required mating dimensions
1 = Mounting clearance
2 = Scale-tape thickness
3 = Distance between floor of scale-tape slot and threaded mounting hole
4 = Reference mark
5 = Permissible axial motion (scale tape relative to scanning head) ≤ ±0.5 mm
6 = Chamfer for accessibility with moiré setting (mounting option Õ)
7 = Distance between scale-tape slot floor and scanning head’s rear mounting surface
8 = Eccentric bushing (Moiré setting)
9 = Holes required for fine adjustment
10 = Mounting clearance (spacer shim)
11 = Space for mounting aid
12 =	Direction for removing the mounting aid (with mounting option Ô)
With mounting option  the mounting aid can also be used from the opposite side
13 = Positive direction of rotation for output signals as per interface description
14 = Scale tape slot floor  D
15 = Floor of pocket is ferromagnetic for fixing the tensioning cleat
16 = Chamfer length > 60 mm
17 = Mounting screw (optional), depends on the required scale-tape tension

12

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

ERA 89x2 scale tape (segment)		 = Length of the arc in the stress-free zone, pay attention to the scale-tape thickness
L = Position of the two end-piece openings or threaded mounting holes
L1 = Traverse path
L2 = Measuring range in the arc
S = Measurement start
D = Slot-floor diameterÞ = Measuring range in degrees (segment angle)

Product Information ERA 7900 Series, ERA 8900 Series   12/2023

13Connecting cable

PUR connecting cable [4(2 × 0.14 mm2) + (4 × 0.5 mm2)]; AP = 0.5 mm2¬ 8 mmComplete with connector (female) andD-sub connector (male) for signal alignment
with PWM 211184705-xx

DR. JOHANNES HEIDENHAIN GmbH
Dr.-Johannes-Heidenhain-Straße 583301 Traunreut, Germany +49 8669 31-0
 +49 8669 32-5061
info@heidenhain.dewww.heidenhain.com

1124690 · 02 · A · 02 · 12/2023 · PDF

This Product Information document supersedes all previous editions, which thereby
become invalid. The basis for ordering from HEIDENHAIN is always the Product
Information document edition valid when the order is placed.
More information:
Comply with the requirements described in the following documents to ensure correctand intended operation:• Brochure: Modular Angle Encoders with Scale Drum or Scale Tape1371806-xx