Overview: Why Nameplate Decoding Drives the Entire Selection
Servo motor selection is fundamentally a thermal and mechanical matching exercise, not a horsepower lookup. The 1FK7 SIMOTICS S motor family is paired almost exclusively with the SINAMICS S120 drive platform, and every nameplate parameter (static torque, rated torque, static current, rated current, maximum speed, feedback, brake, IP class) flows directly into the SINAMICS configuration and the SIZER engineering output. Reading the nameplate correctly is the difference between an axis that runs cool at S1 and an axis that trips I²t or thermal overload on the first cycle. This reference decodes the 1FK7 ordering code, explains the S1 data block, derives the torque constant Kt, and shows how to back the drive current rating out of motor data.
1FK7 Part Number Structure (1FK7083-5AF71-1TA0)
The Siemens 1FK7 ordering code is decoded left-to-right. Each digit or group has a defined meaning, and any substitution can change the mechanical envelope, the winding, the feedback, or the IP rating.
| Code Position | Value (Example) | Meaning |
|---|---|---|
| 1–4 | 1FK7 | 1FK7 SIMOTICS S servo motor product line (synchronous, permanent-magnet, brushless) |
| 5–7 | 083 | Shaft height and length specification. Leading "08" = shaft height 80 (≈80 mm). Trailing "3" = length variant (3 = long frame in the 80 mm height class) |
| 8 | 5 | Compact motor designation within the 1FK7 family |
| 9 | A | Cooling method: A = self-cooled (natural convection on the surface) |
| 10 | F | Rated speed: F = 3000 rpm rated (Nn = 3000 rpm) |
| 11–13 | 711 | Winding / characteristic data block (specific to 1FK7; not customer-facing) |
| 14 | T | Feedback: T = 2-pole resolver (R15-type incremental resolver, two-pole pair) |
| 15 | A | Shaft extension and brake: A = keyed shaft with keyway, without holding brake |
| 16 | 0 | Degree of protection: 0 = IP64 (totally enclosed, dust-protected, splash-proof) |
The trailing position (0) is the one most often misread: a "0" is IP64, while a "1" is IP65 in the same housing. Higher IP ratings (IP65, IP67) require shaft seals and a sealed terminal box, which change the overall motor length and may shift the catalog number to a different length variant. Always re-verify the IP code in the Siemens 1FK7 configuration manual before pulling the motor out of the cabinet.
Mechanical Specification Terminology
Mechanical data on a Siemens servo nameplate is more constrained than on an induction motor. The following terms appear on the 1FK7 data sheet and dimensional drawing, and each must be carried into the mechanical design.
| Term | Definition | 1FK7083-5AF71-1TA0 Value |
|---|---|---|
| Shaft height | Approximate distance from the bottom of the motor foot to the centerline of the output shaft. Used as a frame-size index (IEC 60072 family). | 80 (i.e. 80 mm nominal) |
| Centerline-to-base distance | Half the bolt-hole center distance shown on the dimensional drawing. The actual half-distance is typically a few mm less than the shaft height index. | 77.5 mm (155 mm / 2) |
| Length variant | Stack length / iron-stack code within a given shaft height. Higher numbers = longer stack, higher continuous torque. | 3 (long frame in the 80 mm class) |
| Flange size | Square or rectangular mounting flange, defined by bolt circle and pilot diameter. | Refer to CAD Creator drawing for the 1FK7083 frame |
| Shaft extension | Output shaft detail: keyed/with keyway, plain, or friction-locked (shrink disc / clamp). Affects the allowable radial and axial loads. | Keyed, with keyway (per position 15 = A) |
| Holding brake | Optional spring-set, electrically-released holding brake mounted at the B-end. Adds length, mass, and inertia. Identify by the option code in position 15. | None on this example (A = without brake) |
| Degree of protection | IP code per IEC 60034-5. Defines dust and water ingress rating with the motor installed as specified. | IP64 |
| Cooling method | IC code per IEC 60034-6. "A" position-9 = self-cooled (IC410, surface cooled by free convection). | IC410, self-cooled |
The shaft-height index is a marketing and catalog code, not a measured dimension. Always pull the CAD drawing (DXF/STEP/PDF) from Siemens CAD Creator and dimension from the drawing, not from the catalog number. A common field error is to drill mounting holes to 80 mm and discover after installation that the centerline is 77.5 mm.
Electrical and Thermal Nameplate Data (S1 Continuous Duty)
The S1 data block on the 1FK7083-5AF71-1TA0 nameplate is the foundation of every sizing calculation. All values are referenced to a 100 K winding temperature rise (ΔT = 100 K) above a 40 °C ambient, with the motor mounted as specified (flange or foot) and the heat sink in free air.
| Symbol | Parameter | Value | Unit | Definition |
|---|---|---|---|---|
| M0 | Static torque, continuous | 16.0 | Nm | Continuous torque at standstill (n = 0) with ΔT = 100 K. With the resolver and resolver cable, the motor can hold this torque indefinitely without thermal trip. |
| I0 | Static current, continuous | 10.4 | A | RMS line current required to develop M0 at standstill. This is the key drive-sizing parameter. |
| Mn | Rated torque, continuous | 10.5 | Nm | Continuous torque at rated speed Nn with ΔT = 100 K. Often similar in magnitude to M0 for naturally-cooled 1FK7 servos at 3000 rpm. |
| In | Rated current, continuous | 7.4 | A | RMS line current to develop Mn at Nn. Lower than I0 because back-EMF reduces the current-to-torque headroom at speed. |
| Nn | Rated speed | 3000 | rpm | Speed at which Mn is defined. Field weakening region starts above this point if the motor characteristic permits. |
| Nmax | Maximum permissible mechanical speed | 6000 | rpm | Hard limit imposed by mechanical balance, bearing, and resolver limits. Do not exceed even briefly. |
| n2pk | 2× rated speed (catalog option) | Refer to datasheet | rpm | Maximum operating speed for constant-power field-weakening; not all 1FK7 windings permit operation at 2× Nn. |
Mechanical Output Power at the S1 Point
For a first-pass sanity check, the S1 mechanical output power is calculated as:
P_mech = M_n × 2π × N_n / 60
For the 1FK7083-5AF71-1TA0:
P_mech = 10.5 Nm × 2π × 3000 / 60 = 10.5 × 314.159 ≈ 3299 W ≈ 3.3 kW
Note that M0 at zero speed delivers zero mechanical power; it is purely a thermal / current-rating constraint. The drive must be sized for the current that delivers M0, not for the 3.3 kW figure alone.
Torque Constant Kt and Current-to-Torque Conversion
The torque constant Kt is the linear gain between RMS current and developed torque in the constant-torque region (below base speed):
T = Kt × I
For the 1FK7083-5AF71-1TA0 the published Kt is 1.52 Nm/A. This can be cross-checked against the M0 / I0 ratio:
Kt_check = M_0 / I_0 = 16.0 / 10.4 = 1.538 Nm/A
The small difference (1.52 vs 1.538) is normal: published Kt is typically an average across the operating range and includes resolver offset compensation. Use the catalog Kt in sizing calculations; treat the M0/I0 ratio as a verification check only.
The back-EMF constant Ke (in V per 1000 rpm, line-to-line RMS) is related to Kt by:
Ke = Kt / (√3 × (60 / 2π) × 10⁻³) ≈ Kt × 102.97 → V_peak-line / (1000 rpm)
For this motor, Kt = 1.52 Nm/A gives Ke ≈ 156.5 V/1000 rpm. This is the open-circuit line-to-line RMS voltage at 1000 rpm. The DC-link voltage of the SINAMICS S120 must be high enough to force current into the motor above base speed; the headroom requirement is what bounds the field-weakening region.
Drive (SINAMICS) Current Sizing Procedure
The drive selected must source the motor current at standstill (the worst case for naturally-cooled 1FK7 servos). The selection rule is:
- Identify the application profile: continuous torque at one speed, or cyclic with accelerations and dwells.
- For continuous duty (motor running at one speed/torque in steady state): select a drive whose rated output current is ≥ I0 (10.4 A for the example). Margin of 10–20% is recommended to avoid operating the drive continuously at its thermal limit.
- For cyclic duty with peak torques above the S1 curve (e.g. point-to-point positioning with short acceleration ramps): the drive must supply the peak current and the RMS of the cyclic current over a thermal time constant. Drive Ipeak typically = 1.5× to 2× Irated for ≈ 3 s on SINAMICS S120 Motor Modules; verify in the S120 manual that the Motor Module can deliver the required current profile.
- Confirm that the Motor Module's I0-equivalent (its continuous output rating at the switching frequency used) is ≥ I0. On SINAMICS S120 this is the In value in the S120 configuration manual, derated for switching frequency (4 kHz, 8 kHz, or 16 kHz). Many S120 Motor Modules derate by 20–50% when switched at 8 kHz versus 4 kHz.
- Verify that the motor and drive share a common DC bus voltage class. 1FK7 motors with the "71x" winding block are typically matched to 3-phase 400 V class SINAMICS S120 (400–480 V line) on a 600 V DC bus. Do not mix 230 V and 400 V class motors and drives.
Duty Cycle Analysis: S1 Curve vs RMS Torque
Most real axes are not steady-state. The torque/speed curve shows higher torque available above the S1 characteristic for short durations, with the trade-off that the cycle's RMS torque must fall below the S1 curve at the average speed. The procedure is:
- Discretize the motion profile into segments (accelerate, constant speed, dwell, decelerate, dwell).
- For each segment, record the average torque Ti and the segment duration Δti.
- Compute the equivalent RMS torque across the cycle:
T_rms = √( (T₁²·Δt₁ + T₂²·Δt₂ + … + Tn²·Δtn) / (Δt₁ + Δt₂ + … + Δtn) )
- Compute the cycle's average speed n_avg.
- Plot the point (n_avg, T_rms) on the motor's torque/speed curve. The point must lie on or below the S1 characteristic at that speed. If it does, the motor can deliver the cycle thermally. If it does not, choose a longer stack, force cooling, or reduce the cycle load.
For the 1FK7083-5AF71-1TA0 at n_avg = 3000 rpm, the cycle RMS must satisfy T_rms ≤ M_n = 10.5 Nm. At 1500 rpm (half base speed) the S1 limit is still M_n (the naturally-cooled 1FK7 S1 curve is essentially flat below base speed, with the constraint becoming M_0 at standstill).
The same logic applies to current. Define the cycle RMS current I_rms, and select the drive so that its rated I (derated for switching frequency) is ≥ I_rms, while its peak current capability is ≥ I_peak during each segment.
SIZER for Siemens Drives — Configuration Workflow
For a complete drive package, including line filter, line reactor, Motor Module, Control Unit, cabling, and braking resistor, use the SIZER for Siemens Drives engineering tool. The workflow is:
- Open SIZER and create a new project for the SINAMICS S120 line.
- Enter the line-side conditions: supply voltage (e.g. 3 AC 400 V), line frequency, short-circuit capacity, and any line-side options (line filter, line reactor).
- Add the drive line-up: infeed (Active Line Module, Basic Line Module, or Smart Line Module), DC bus, and Motor Module(s).
- Insert the motor. For a Siemens 1FK7083-5AF71-1TA0, the catalog number is recognized by SIZER and the S1 data is auto-populated. Verify the four S1 data points: M0, I0, Mn, In, plus the speed, torque, and current limits.
- Enter the mechanical load data: load inertia reflected to the motor, friction torque, gravity torque (for vertical axes), and any external process torque.
- Enter the motion profile: distance, velocity, acceleration, deceleration, dwell, and cycle time. SIZER computes the RMS torque and the peak torque and overlays the result on the S1 curve.
- Select the Motor Module. SIZER will propose a list of Motor Modules whose In ≥ I0 and whose Ipeak ≥ Ipeak. Confirm the switching frequency and re-validate.
- Export the bill of materials and the SINAMICS configuration. The output is a configured S120 line-up that the commissioning engineer can download to the drive.
CAD Creator and Mechanical Drawings
Mechanical envelope, shaft height, flange dimensions, pilot diameter, bolt circle, and keyway size are all defined by the dimensional drawing, not by the catalog number alone. The drawing is available through Siemens CAD Creator as a 2D PDF and as native 2D/3D CAD (DXF, STEP, IGES, Pro/ENGINEER, Solid Edge, SolidWorks, etc.). For the 1FK7 family, drawings are organized by shaft height. Pull the drawing that matches the exact MLFB of the motor you are ordering; do not substitute a different length variant. For cabinet layout, also confirm:
- Connector or terminal box position and orientation
- Cable entry direction and minimum bend radius for the power and signal cables
- Resolver / encoder cable gland size and EMC routing requirements
- Mounting surface flatness and runout per the Siemens installation guideline
Verification Checklist Before Releasing the Order
| Check | Action | Pass Criterion |
|---|---|---|
| MLFB decoded | Confirm each of the 16 positions against the order | Matches the application specification exactly, including IP code and brake option |
| Drive In ≥ I0 | Look up the SINAMICS Motor Module rated current (derated for the chosen switching frequency) | In,drive ≥ 1.1 × I0 for continuous-duty, ≥ I0 for cyclic-duty with verified RMS |
| RMS torque check | Plot (n_avg, T_rms) on the S1 curve | Below or on the S1 line at n_avg |
| Peak current check | Verify Ipeak of the Motor Module for the cycle peak duration | Drive Ipeak ≥ application Ipeak for the required duration |
| Mechanical envelope | Pull the CAD drawing for the exact MLFB | Shaft height, length, flange, and keyway all match the mechanical design |
| Thermal environment | Confirm mounting (flange, foot, or through-bolt), ambient temperature, and altitude | Site derate is within the 100 K envelope; reduce continuous torque if not |
| Feedback compatibility | Confirm the drive side supports the resolver / encoder type on the motor | SINAMICS S120 Sensor Module supports the motor feedback (e.g. SMC20 for 2-pole resolver) |
| Brake option | Confirm whether the axis needs a holding brake (vertical axis, gravity load) and the correct 24 V supply and logic interface | Brake holding torque ≥ worst-case gravity torque with the required safety factor |
Troubleshooting Matrix: Common Sizing Errors
| Symptom | Most Likely Cause | Corrective Action |
|---|---|---|
| Drive trips F30001 (overcurrent) on first acceleration | Drive rated current < motor Ipeak needed for the load acceleration | Select a higher-rated Motor Module, or reduce load inertia / accel ramp |
| Drive trips F30005 / I²t on a running cycle | Cycle RMS current exceeds drive rated current; or motor RMS torque exceeds S1 at the average speed | Re-plot (n_avg, T_rms); reduce accel/decel, increase dwell, or upsize the motor/drive |
| Motor trips thermal model (F07011 / motor temperature) without drive trip | Motor RMS torque exceeds S1 at standstill (M0 held too long with no cooling air) | Reduce standstill torque duty; add forced-air cooling; upsize to longer stack |
| Axis follows command but position loop is unstable / oscillates | Drive / motor Kt incorrect in commissioning; or feedback type mismatch | Re-enter motor data from the configuration manual; verify the Sensor Module matches the resolver / encoder |
| Maximum speed is below the application requirement | Selected winding has Nmax < the application's maximum speed; or the drive is in torque mode with no field-weakening profile | Choose a 6000-rpm-rated 1FK7 winding and re-validate the SINAMICS S120 current profile in the field-weakening region |
| Mechanical coupling misalignment / premature bearing failure | Shaft height code treated as the actual centerline dimension | Use the CAD Creator dimensional drawing; re-machine the mounting surface to the drawing's centerline value (e.g. 77.5 mm for the 1FK7083, not 80 mm) |
Field-Proven Caveats
Three points are worth flagging explicitly for first-time users:
- The position-9 code on the 1FK7 distinguishes self-cooled ("A") from forced-air-cooled ("B"). Self-cooled motors are quieter and simpler but have a lower M0 at standstill with no shaft rotation. If the application holds torque at standstill for tens of seconds (clamp, tension, vertical hold), a forced-air-cooled variant or a longer stack is usually required.
- Position 15 (shaft + brake) is the easiest place to make a costly mistake. "A" = keyed, no brake; "B" = keyed, with holding brake. The holding brake is a spring-set, electrically-released design. It is not a working brake; it is for holding only. The dynamic braking is done by the drive through the resistor or regenerative feedback.
- Position 16 (IP code) also changes the connector and cable gland. IP65 may require a sealed M17 or M23 Speed-Connector with the matching cable. Confirm the cable type and length against the SIZER BOM before ordering separately.
FAQ
What does the 1FK7083-5AF71-1TA0 part number actually tell me?
The first four characters identify the 1FK7 SIMOTICS S servo family. The next three ("083") specify shaft height 80 mm and length variant 3 (long frame). The "5" is the Compact motor class, "A" is self-cooled, "F" is 3000 rpm rated speed, "T" is a 2-pole resolver, "A" is a keyed shaft with no holding brake, and "0" is IP64. Always confirm every position against the Siemens 1FK7 configuration manual for the exact MLFB.
How do I size the SINAMICS drive from the motor nameplate?
Use the static continuous current I0 (10.4 A for the 1FK7083-5AF71-1TA0) as the floor for the drive's continuous rated output, derated for the chosen switching frequency. For cyclic duty, also verify that the Motor Module's peak current capability covers the cycle's Ipeak for the required duration, and that the cycle's RMS current is below the drive's continuous rating.
What is the difference between M0 and Mn on the 1FK7 nameplate?
M0 is the continuous torque available at zero speed with a 100 K winding temperature rise. Mn is the continuous torque at the rated speed Nn, also at 100 K. For the 1FK7083-5AF71-1TA0 they are 16.0 Nm and 10.5 Nm respectively. M0 is what the drive current rating must support; Mn is the S1 point used in RMS duty-cycle verification.
How is the torque constant Kt used in sizing?
Kt converts RMS current to developed torque in the constant-torque region (T = Kt × I). For the 1FK7083-5AF71-1TA0, Kt = 1.52 Nm/A, so 10.4 A produces ≈ 15.8 Nm at standstill, consistent with M0. Above base speed, the back-EMF reduces the available torque from the same current, which is why the SINAMICS S120 field-weakening model is required for high-speed operation.
Why does the shaft height code (80) not match the actual centerline height (77.5 mm)?
The shaft height is an IEC frame-size index, not a measured dimension. The 77.5 mm is the half-distance of the 155 mm bolt-hole center distance on the mounting flange. Always pull the dimensional drawing from Siemens CAD Creator for the exact MLFB before machining the mounting surface.
Can I use the S1 curve for a cyclic motion profile?
No. The S1 curve is a steady-state thermal limit. For cyclic motion, compute the cycle's RMS torque Trms = √(Σ Ti²·Δti / Σ Δti) and the average speed n_avg, then plot (n_avg, Trms) on the torque/speed curve. The point must lie on or below the S1 line at that speed, otherwise the motor will trip on thermal overload.
Which Siemens tool generates the complete drive bill of materials?
SIZER for Siemens Drives is the engineering tool that sizes the SINAMICS S120 line-up (infeed, Motor Module, cables, filters, braking resistor) and exports a configured BOM from a single project. Use it in conjunction with the Siemens Industry Online Support (SIOS) configuration manuals for the 1FK7 motor and the SINAMICS S120 drive.