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HD25 Industrial Rugged Metal Optical Encoder

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  • NEMA size 25 package
  • Anodized milled aluminum housing with O-ring housing seal
  • LED and phased array wide-gap monolithic encoder technology
  • 64 to 10,000 cycles per revolution (CPR)
  • 256 to 40,000 pulses per revolution (PPR)
  • 2 channel quadrature squarewave outputs
  • Single-ended or differential outputs
  • Optional index (3rd channel)

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 clear anodizing, conforms to the...

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Product Specifications


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
Storage Temperature -40C to 100C

98% non-condensing
100% condensing (NEMA IP65)
Vibration (5 to 2kHz) 20G
Shock, 11 mSec 60G
Electrostatic Discharge 
Single-ended (-S version), IEC 61000-4-2
Differential (-D version), Human Body Model

± 4 kV
± 2 kV
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
  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 Total Indicated Runout 0.0003 in.
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
  • Specifications apply over 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
  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  
PinQuad. (AB)
A A channel
B B channel
C* Index
F Common
G Case ground

* Only available when Index channel is specified.

The 7-pin Connector


PinQuad. (AB)
A A+ channel
B B+ channel
C* Index+
F Common
G Case ground
H A- channel
I B- channel
J* Index-

* Only available when Index channel is specified.

The 10-pin Connector


Title Date Description 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.

Product Description

Restriction of Hazardous Substances

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 clear anodizing, conforms to the industrial standard size 25 package. Size 25 encoders are widely used and are considered to be 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. The HD25 is a factory stock product with little or no lead-time.     

Typical applications include:

  • Automation, robotics, motion control, elevator controls, machine tools, food processing, X-Y tables and conveyors.
  • Lathes, grinders, CNC machine tools, high performance servos, test equipment, packaging machines, balance machines and cutting machines.
  • Web processing, rotary tables, transfer machines, stacker cranes, press controls, printing presses and pump controls.
  • Oil field equipment, saw mill machinery and construction machinery.

Our absolute encoders may be used in many stand alone applications that do not require a PC interface. For these applications we provide detailed communications protocols for all of our absolute products (see the SEI Absolute Encoder Communications Protocol page).

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.

Cable/connector assembly not included and must be ordered separately.

Related Products & Accessories

Product Configuration

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1. CPR
2. Flat

3. Seal

4. Voltage

5. Index

6. Output

Product Part Number

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For purchasing or volume discounts, please use the above part number and contact us at: or

800.736.0194 (Toll Free)
360.260.2468 (Local)