HD25 Industrial Rugged Metal Optical Encoder

HD25 Features

  • NEMA size 25 package
  • Anodized black aluminum housing
  • 64 to 10,000 cycles per revolution (CPR)
  • 256 to 40,000 pulses per revolution (PPR)
  • 2-channel quadrature output with optional index
  • Single-ended or differential outputs
  • Sealed IP65 option

See more info below

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HD25 Product Description

The HD25 is a rugged optical incremental shaft encoder designed for heavy-duty industrial applications. The housing, machined from a solid billet aluminum block and finished with black anodizing, conforms to the industrial standard size 25 package. Size 25 encoders are widely used and considered the backbone of feedback devices found in factory automation and industrial applications. The HD25 will drop directly into existing applications to provide a superior solution at a competitive cost.

Product Specifications

View here or download the specifications


Parameter Value

Operating Temperature
  Low voltage version, CPR < 3600
  High voltage version, CPR < 3600
  Low voltage version, CPR ≥ 3600
  High voltage version, CPR ≥ 3600

-40C to 100C
-40C to 85C
-25C to 100C
-25C to 85C

98% non-condensing
100% condensing (NEMA IP65)
Vibration (10 to 2kHz, sinusoidal) 20G
Shock (6 milliseconds, half-sine) 75G
Electrostatic Discharge 
Single-ended (-S version), IEC 61000-4-2
Differential (-D version), Human Body Model

± 4 kV
± 2 kV


Parameter Value
Size NEMA size 25
Housing and Cover Material Anodized aluminum
Shaft Material Stainless steel
Weight 17 oz.
Shaft Diameter 0.3748 in. (+0.0000 in. -0.0003 in.)
Shaft Optional Flat Size .08 in. long x .03 in. deep
Max. Acceleration 100000 rad / sec²
Max. Shaft Speed (1)
  Non-sealed (mechanical)
  Sealed  (mechanical)

15000 rpm
6000 rpm
Shaft Torque

< 0.5 in-oz
3.5 in-oz typical
Max. Shaft Load

40 lb.
35 lb.
Max. Shaft Runout 0.0003 in. T.I.R.
Bearing Life @ 4 Pound Load 2.3 x 10^9 revolutions
Moment of Inertia 2.8 x 10^-4 oz-in-sec²
Technical Bulletin TB1001 - Shaft and Bore Tolerances Download

(1) The maximum speed due to electrical considerations is dependent on the CPR. See the EM1 and EM2 product pages.


B leads A for clockwise shaft rotation, and A leads B for counterclockwise rotation viewed from the shaft side of the encoder.


  • Specifications apply over the entire operating temperature range.
  • Typical values are specified at 25°C.
  • Output driver IC: ET7272B
  • For complete details, see the EM1 and EM2 product pages.
Supply Voltage (Vs)
  Low Voltage Version
  High Voltage Version




Supply Current     138 mA  
Low-level Output    0.4 0.5 V IOL = 20mA
High-level Output    Vs - 2.0   V IOH = -20mA
Output Rise/Fall Time    700 980 nS


A A channel
B B channel
C Index
E Case ground
F Common


A A+ channel
B B+ channel
C Index+
F Common
G Case ground
H A- channel
I B- channel
J Index-


Title Date Description Download
HB5M, HB6M & HD25 - PCN 7315 5/17/2023 As part of our ongoing continuous improvement efforts, we are updating our HB5M, HB6M and HD25 series of optical encoders to make product labeling clearer and permanent. The aluminum housing of these encoders will now be anodized black, and labeling will be laser etched onto the surface, providing more contrast and legibility. Previously pin-outs were machined into the housing and product labeling was printed onto an adhesive label that was placed on the side of the product. Product labeling will also now appear on the top surface of the encoder near the pin-out labeling. Download
EM1 & EM2 Update - PCN 4199 1/14/2014 Based on our continuous process improvement program, US Digital is changing the current marking method for our EM1 and EM2 encoder modules to a serialization method. This change will allow for each module to have a unique code; the current marking method is based on a date code system that includes all encoder modules produced within a specific week / year. The serialization system will be based on a hexadecimal system. Download
EM1 LED Die - PCN 1016 2/7/2013 As part of US Digital's continual assurance of supply strategy, we have qualified additional sources for our LED die used in our EM1 encoder module, which in turn impacts all of the following products:

EM1, E2, E3, E5, E6, H1, H15, H3, H5, H6, HB5M, HB6M, HD25, PE, S1, S2, S5, S6, T5 and T6

The device specification will remain the same, i.e. there will be no change to form, fit or function of the product(s) as specified by US Digital. The appropriate quality and reliability testing has been performed on representative products to ensure normal parametric distribution, consistent with US Digital's quality and reliability standards.

Additional Information

Product Notes

  • Cables and connectors are not included and must be ordered separately.
  • US Digital® warrants its products against defects in materials and workmanship for two years. See complete warranty for details.


Guides and Additional Documentation


3D Model Downloads

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