QD145 Incremental Encoder IP-66 Sealing Option

Quantum Devices Inc. has a mounting option that allows for IP-66 sealing of the QD145 Incremental Encoder.  There are two o-rings in the clam shell design; One o-ring seals the encoder to the mounting surface (usually a motor), and the other o-ring seals the end bell housing that covers the encoder.  This is a popular, inexpensive, option for customers who may not need the IP-66 sealing,  but want some sort of end bell protection over the encoder.

Cross-referencing RENCO Incremental Encoders

We have always been able to come up with a suitable replacement for Renco encoders, but our customers are making us aware that we need to point that out.

For those who don’t know, Renco, after being absorbed by Heidenhain, made the decision to  eliminate much of their product line.  This move has left quite a few of their customers in the lurch. To help fill this need, we recently started promoting our ability to cross-reference Renco encoder lines on our web site with the rather obvious image you see above.  Clicking on this image will take you to a request form where you can let us know which Renco Encoder you are trying to cross.

Keep in mind that we can cross other encoder manufacturers as well.

As a  general reference, the following Renco incremental encoder cross-reference table can show you which style of Quantum Devices Incremental Encoder will likely work best.

Renco Encoder Quantum Devices Encoder
RHS15 QD145 or QR12
RCM15 QD145 or QR12
RM15 QD145 or QR12
RCH20 QD145 or QR12 or QD200
RHS20 QD145 or QR12 or QD200
RM21 QD145 or QR12 or QD200
RCM21 QD145 or QR12 or QD200
RCH50 QD145 or QD200
R50i QD145 or QR12 or QD200
R35i QR12 or LP12
R22i QR12 or LP12
RA25 QDH20
RS25 QDH20

The use of potentiometers in Incremental Encoder Design

Recently I decided to catalog the competitive Incremental Encoders that have populated the shelves surrounding my desk.  In doing so, I was surprised to find that many of our competitors use potentiometers in their designs.

I can understand why they need to use potentiometers.  In most designs the potentiometers are used to balance the raw analog signals produced by the Incremental Encoder sensor.   A potentiometer is the perfect component for this, you fire up the Incremental Encoder during test, lay a scope probe on it and dial the value specified by Engineering.  For most encoder designs, the only other option is to guess at some resistor values hoping that you don’t have to solder and unsolder resistors too many times until you hone in the correct signal, as that would be a very time consuming process.

While I can understand the use of Potentiometers, the reason that I am a bit shocked by their ubiquity in competitor’s designs is that potentiometers are inherently a much less reliable component.  A resistor is all one solid piece, but a potentiometer (which is a variable resistor) has a resistive track and a movable wiper that slides along to vary the resistance value. Moving parts are inherently less reliable than a non-moveable part.

Here are a few of the PCBs from various manufacturers ,  the potentiometers are circled in Red:


This next one is my favorite.  Thirteen potentiometers!

I am proud to say that Quantum Devices Encoders do not use potentiometers in their Incremental Encoder designs.  The reason we can avoid potentiometers is because of our patented phased array sensor that provides perfectly balanced complementary signals right from the sensor.

Other incremental encoder sensors suffer from having their active areas in different locations along the length of the sensor. Since the light source spreads light unevenly over the sensor, some active areas receive more light than others creating signal imbalances.

In Quantum Devices Incremental Encoders the photosensitive areas of each channel are interlaced with each another,  so all active areas receive the same amount of light.  This eliminates the need to balance any signals, which in turn eliminates the need for potentiometers in the design.

Below is an drawing of the phased array sensor Red indicates Channel A active areas, Blue indicates channel B active areas.

Inverted Flex Mount for QD145 Optical Encoder


.Another way to mount an Optical Encoder

Instead of using an end bell,  a lot of our motor manufacturer customers recess the QD145 optical encoder into an extended motor housing and then seal the motor with an end plate.

This has the advantage of being a lower cost item to manufacture, as the  motor housing is often extruded  or cast.  Just making the housing longer and providing an end plate usually costs less than casting a separate end bell.

Conventional Motor End Bell

But the downside to a recessed motor housing is that mounting an optical encoder in a recess like this creates a problem when tightening the set screws to the shaft. It often has to be done through an MS connector hole, or blind, by reaching the Allen wrench around and under the encoder.

Cast recess in motor housing

Because of this, we occasionally get asked for a a version of our QD145 optical encoder that allows the assembler to  access the set screws above the body of the encoder.  The inverted flex mount turns the encoder upside down allowing easy access to the set screws that are normally underneath the encoder.

The QD145 inverted flex mounti9ng option is not currently listed on our web site, but can be ordered using the following part numbers under the mounting options:

Use an 06 Mounting option for the inverted 1.157″ Bolt Circle flex mount.

Use an 07 Mounting option for the inverted 1.812″ Bolt circle flex mount.

The wiring is changed internal to the encoder so that the QD145 maintains correct phasing for all channels.

Another option for a drop in recess mounted encoder is the JR12 Jam Nut style encoder which does not use set screws to secure the encoder to the shaft, but a compression nut instead.

Dimensions for the 07 version of the QD145 Inverted flex mount.

Understanding Incremental Encoder signals

Which incremental encoder wires should I use?

Channels A & B (Incremental Channels)

Use only A (or only B) for an RPM or counting applications where the rotation is either unidirectional, or where you don’t need to know direction.

Use A and B together to know direction. After two low pulses the next high pulse indicates direction.  This is due to the phasing offset between A and B of 90 electrical degrees, placing the signals in what is known as quadrature.

These signals can also be used to set up an up/down counter

Index pulse, also known as Z, marker, or I

Index pulse is a pulse that occurs once per rotation. It’s duration is nominally one A (or B) electrical cycle, but can be gated to reduce the pulse width.

The Index (Z) pulse can be used to verify correct pulse count

The Incremental Encoder Index pulse is commonly used for precision homing.  As an example, a lead screw may bring a carriage back to a limit switch.  It is the nature of limit switches to close at relatively imprecise points. This only gives a coarse homing point. The machine can then rotate the lead screw until the Z pulse goes high.

For a 5000 line count encoder this would mean locating position to within 1/5000 of a rotation or a precision of .072 Mechanical Degrees.  This number would then be multiplied against lead screw travel.

Commutation (UVW) signals are used to commutate a brushless DC motor. I always like to compare these signals to that of a distributor in a car. The commutation (sometimes called “Hall”) signals tell the motor windings when to fire

You would need to have encoder commutation signals if the motor you are mounting the encoder to has a pole count and there is no other device doing the work of commutation.  It is important to note that commutation signals need to be aligned or “timed” to the motor.

Single ended VS differential

These terms refer not to the waveforms of signals, but instead to the way the signals are wired.

Single ended wiring uses one signal wire per channel and all signals are referenced to a common ground.

TTL and Open Collector are types of single ended wiring.

Differential wiring uses two wires per channel that are referenced to each other.  The signals on these wires are always 180 electrical degrees out of phase, or exact opposites.  This wiring is useful for higher noise immunity, at the cost of having more electrical connections.

Differential wiring is often employed in longer wire runs as any noise picked up on the wiring is common mode rejected.

RS-422 is an example of differential wiring.


Understanding Options on the QDH20 Industrial Rotary Encoder.

The QDH20 is an IP66 sealed encoder made for the rugged duty of an industrial application.  Due to the huge array of configuration options, this optical encoder has over 200,000  possible ways that it can be configured.

While this is certainly an advantage to an end user that may be seeking just the right encoder, the sheer number of choices can make configuring a part number a confusing proposition.  I am going to try to shed some light on the QDH20’s available choices in order to make things a bit more clear.

Mounting Options:

This refers to the style of the mounting “face” of the encoder.  There are three basic types: Flange, Servo and Flex mount.  These size of each of these types are referred to by motor sizing terminology. A “Size 20” mount is approximately two inches and a “Size 25” is about 2.5 inches.

The flange mount is used when you are bolting directly to a surface. The flange surface is typically square with bolt holes in each of the four corners.

I am using CAD drawings for my examples as they are more readily available and easier for me to work with than photos.

The servo mount is typically round and there is a built in retaining groove around the mounting edge. While it can be mounted using this edge, there are also three tapped mounting holes for the size 25 and a set of three and as set of four tapped mounting holes for the size 20, drilled into the face of the Servo mount.

The flex mount  has a spring steel mounting that allows for misalignment between the encoder and whatever it is mounted to. This is used with a “hollow shaft” option where the QDH20 encoder is receiving a shaft.

Mounting options may include a “pilot” or boss that is used to help align the encoder to a mounting surface. These are either female, which are recessed into the encoder housing, or male, which protrude out from the encoder housing.

Quick mounting summary:
For QDH20 Mounting options you can have a hollow shaft which can only be a flex mount, or a standard shafted encoder which can be either a flange mount (square) or a servo mount (round).

Both of these configurations may have either a male or female pilot.

Hollow shaft QDH20 encoders always have a flex mount and do not have a pilot.

Connector Housing Options:

The housing of a QDH20 encoder has two main considerations; the style of electrical connection to the encoder, and the way these electrical connections exit the encoder.

Electrical connections for the QDH20 encoder can be either a MS (Military Style) connector, or a flying leads type connection, referred to as a “wire gland”

The MS Connectors have three sizes 10 Pin, 7 Pin and 6 Pin.  The number of output signals needed determines these connector sizes. For  one channel single ended applications  a six pin connector will work just fine, but for an application where all channels ( AB &Z ) and their complements are needed a ten pin MS Connector is a must.

Note that while it is possible to make an encoder that has  a single output with a ten-pin connector, items like these are not part of the QDH20 standard offering. If a special QDH20 configuration is needed, Quantum Devices’ crack engineering team will typically be able to make it happen.

Both styles of electrical connections can exit the encoder either axially, or along the same axis as the encoder’s shaft, or radially, perpendicular to the shaft.   Being able to choose this electrical connection exit method allows for the QDH20 encoder to fit into tight spaces.

Shaft Options:

Shafts options will either be a standard solid shaft or a hollow shaft.  Keep in mind that the solid shafts  go with the servo and flange style mount and the hollow shaft has a flex style mount.

Resolution options:

The QDH20 encoder currently can have resolutions (pulses per rotation) of up to 5000 direct read. (not interpolated).

The current QDH20 resolution options are:
200, 250, 256, 500, 512, 600, 1000, 1024, 1250, 2000, 2048, 2500, 3600, 4096 and 5000

These resolutions are all “direct read”, which means that the signals are taken right from the encoder disk, as opposed to interpolation which creates more pulses than are represented by the disk pattern.  Direct read is always preferred if you can get it as there is one less error factor (Interpolation error) to worry about.

Output Options:
The  electrical output that the QDH20 encoder can provide are either 5 to 26 Volt differential or single ended via the  OL7272 line driver, or an Open Collector style.

The OL7272 has thermal and electrical overload protections built into it.   The encoder is designed so that whatever voltage you put into the power rails you get out, minus a small voltage drop, on the signal wires.

Open collector style encoders require pull up resistors to make the signals work.

Channel Options:

This is used to select the style and number of output channels you need.   This is the option that drives the style of connector the QDH20 will have.

Output Waveform Options:

This option refers to the phasing relationships between the encoder channels.  Some encoder manufacturers have established traditional waveforms styles that their industrial encoders fall into.

The QDH20 Waveform options 01 and 02 match exactly with certain BEI style encoders. QDH20 waveform options 03 and 04  match up with certain EPC style encoders.

While the many ways  to configure a QDH20 encoder can be confusing, hopefully looking at each option has made it a bit simpler to understand.

The robust QD-H20 IP-66 Industrial Rotary Encoder



The QD-H20 is an idea replacement encoder for size 20 and size 25 industrial applications.  It is an IP-66 sealed rotary incremental encoder.  This high IP rating provides outstanding environmental protection with all of the line count and output options of the QD-145 incremental encoder.

The QDH20 style Industrial Rotary Encoder is typically used in applications such as Machine Control, Process Control, Elevator Controls, Agricultural Machinery, Textile Equipment, Robotics, Food processing, Conveyors, Material Handling, as well as, any application where water/contaminant ingress or durability is a concern.

The QD-H20 Incremental Encoder has three styles of MS connectors, 6,7, and 10 pin, along with a flying lead option, and the ability to come with custom cable lengths.  Each connector option is possible in radial and axial configurations.

The QD-H20 Rotary Encoder boasts a wide –20 to 100 Deg. C temperature range and a 500kHz frequency response.  Multiple shaft sizes ranging from .250” to .650” in both hollow and solid shaft are available.

The rugged dual bearing set allows the QD-H20 industrial rotary encoder to handle overhung loads, such as direct mount pulleys, with side load forces as high as 40 pounds nominally and 80 pounds maximum.

More information can be found at the Quantum Devices main site at http://www.quantumdev.com/products/optical_encoders/qdh20.html

A PDF of the QD-H20 encoder specifications can be downloaded directly at http://www.quantumdev.com/pdf/qdh20.pdf

Quantum Devices Inc. is a leading manufacturer of Rotary incremental encoders. They can assist in encoder selection and can be reached at (608) 924-3000 or via E-mail