faqs about products and applications at LTN

FAQ resolvers

Important information on frequently asked questions relating to products and applications

Frequently asked questions on resolvers

What is a resolver and what is it used for?

Resolvers are contact-free, inductive angle feedback systems providing an absolute signal. They are mainly used for controlling the rotational speed of servo motors. Compared to rotary encoders, resolvers are suitable for a much broader spectrum of applications. The operating temperature ranges from -196°C to 155°C, depending on the design. Resolvers are practically impervious to radioactivity and can be employed in an absolute vacuum (outer space). Rotational speeds up to 90,000 rpm can be controlled.

How is the stator of a resolver mounted?

The stator is flanged to the motor’s bearing shield. Clamps or retaining rings are used for this purpose.

How is the rotor of a resolver mounted?

The rotor is generally glued to the shaft. Loctite® is frequently used for this purpose. Some geometries or safety applications require the rotor to be fixed to the shaft using an axial screw. With larger shaft diameters, the rotor is secured with a radial clamping screw (e.g. a headless screw).

Why do you provide two or three data tables in one data sheet?

The servo controllers which are currently available in the market employ individual frequencies and voltages to communicate with resolvers. The three tables show the various resistances and phase shifts for two or three different input frequencies and feed voltages. These tables are meant to provide the user with a guideline for selecting the correct resolver or the appropriate control unit.

Please compare the transformation ratio, the input voltage and the current consumption with the specifications for your control unit. Hint: A higher current consumption implies reduced sensitivity to electromagnetic interference.

How is the rotor aligned to the stator?

Please refer to the procedure described in the manual for your control unit for information on calibrating your measuring system.

Most of our resolvers contain a visual marker for the zero position. If not, the zero position can also be determined using an oscilloscope. Modern servo controllers normally carry out the fine calibration automatically.

During first use the resolver control unit reports an error

Possible causes:

a. Do the frequency, input voltage, transformation ratio and current consumption values of the resolver match the specifications for the control unit?
b. Is the resolver correctly connected to the control unit?
c. Are the rotor and stator correctly aligned (see data sheet)?
d. Is there any electromagnetic interference (electric motor brake, long control cables in a room full of motors)?
Possible remedies:
d.1. Twist the wires (input voltage, sine, cos)
d.2. Shield the wires
d.3. Shield the motor brake with an aluminium bearing shield at the NDE
d.4. Interrupt the magnetic flux with an non-magnetic resolver hub
d.5. Ask for on-site assistance with the development of your motor

Why does the encapsulated, self-contained resolver system use a spring as a torque support?

Our encapsulated, self-contained resolvers contain two high-grade ball bearings. If these were to be firmly interlocked with the motor shaft, it would not be possible to compensate any production tolerances. The bearings would be destroyed. The encapsulated system has to move freely on the shaft in the radial direction.

We use a control unit made by “Lenze” – are all resolvers compatible?

No. “Lenze” employs two different feedback mechanisms. Please get in touch with us indicating the exact type of your control unit. We will then select the appropriate resolver for your Lenze control unit.

Your standard resolver is mechanically incompatible with our motor and its electrical characteristics don’t match our control unit.

We keep a very wide range of resolvers with special characteristics in stock to satisfy all customer or application demands. Please provide us with the required installation dimensions (e.g. a technical drawing or a STEP file) or the data sheet for your control unit. We will then select the appropriate resolver for you.

Our control unit is only designed to use encoders but we would like to mount a resolver. Is this possible?

Yes. LTN provides various encapsulated resolver systems which can take the place of an encoder system. You can find the dimensions of the connection flange in the data sheets for our R36, R58 and R71 type resolvers. Incremental or absolute resolver signals can be supplied to your system quickly and easily using our resolver-to-encoder transformer boards (G-REC, G-RDC or G-RCC).

We build multi-pole motors. Can you help?

LTN provides a number of resolvers for direct commutation of motors with 2, 4, 6, 8 or 10 poles. The number of pole pairs on the resolver should generally correlate with the number of motor poles. For example, a motor with 8 poles can be commutated directly with a 4-speed resolver. However, most control units can use a standard resolver with a single pole pair to control the rotational speed with adequate accuracy.

How accurate are resolvers?

By default, resolvers achieve an absolute measurement accuracy of ±10‘. In most cases this accuracy is sufficient for rotational speed control units provided the system exhibits normal inertial properties. Greater accuracy may be required for positioning tasks. LTN can also supply resolvers with ±6‘ or ±4‘ absolute accuracy for such applications.

Do resolvers need a reference point?

No, resolvers do not need a reference point. This is their chief advantage compared to conventional incremental encoders. Resolvers provide the absolute position of an axle with arcminute accuracy immediately after switching on.

Where can I find information on the configuration (colour code) of the individual wires?

You can find this information in the data sheets. There is no accepted standard for colours and designations, though a semi-official standard is used internationally:

R1 = +ref = red-white
R2= -ref = black-white (although R3 and yellow-white are also used)

S1 = +cos = red
S3 = -cos = black

S2 = +sin = yellow
S4 = -sin = blue

What happens if the specified rotational speed is exceeded?

The specified maximum rotational speed includes a certain safety factor. If this is exceeded, there is a danger that the laminated cores and the rotor windings may no longer be strong enough to withstand centrifugal forces and that the resolver will be destroyed. This particularly applies at high temperatures, where the adhesion of the glues and resins is reduced. Please get in touch with us if your application requires rotational speeds exceeding those specified in the data sheet.

Why do you not provide an MTBF for resolvers?

Non-encapsulated resolvers contain no moving or wearing parts. Even after several years of endurance testing at elevated temperatures, no failures were observed that might be relevant for MTBF calculations. In addition, reports from our customers about field failures are too seldom and lacking in detail to allow an MTBF to be calculated.

What information should be included in an enquiry?

In order to provide you with a timely and reliable answer, we provide a form for enquiries on our homepage. Please enter all typical data and the most important parameters needed for the specification of resolvers in this form. You may download this form here.

How and at what times can I contact LTN customer service?

You can contact our customer service department by email (ltn (at) ltn.de) or by phone (+49 8024 6080-0), Monday to Thursday 8am to 5pm and Friday 8am to 3pm.

Please don’t hesitate to contact us if you have any questions