EL7211 — Calculation of Actual Torque (MDP742 mode)

Posted by on

EL7211 — Calculation of Actual Torque (MDP742 mode)



Scope / Note:
The formulas below apply when the EL7211 drive is operated using the MDP742 communication method.

Registers / Definitions

  • Torque feedback (raw): 0x6010:08 — Display of current torque value.

    • This value is expressed in 1/1000 (per-mille) of the rated current (i.e., a raw integer where 1000 represents 100% of rated current).

    • Denote this raw value as T_raw (unit: per-mille, i.e., ‰).

  • Rated current: 0x8011:12 — Rated current of the motor/drive.

    • Denote as I_rated (unit: A).

  • Torque constant: 0x8011:16 — Torque constant used to convert current to torque.

    • Denote as K_t (unit: Nm/A or the unit indicated by the drive/motor datasheet — confirm in the manual).

  • Mode selection (current interpretation): 0x8010:54

    • If TRUE → average (RMS) current interpretation.

    • If FALSE → peak current interpretation.

Conversion principle (concept)

  1. Convert the raw per-mille torque feedback to actual current (A).

  2. Multiply the resulting current by the torque constant K_t to obtain torque in Nm.

Formulas

1) When 0x8010:54 = TRUE (Average / RMS current mode):

Imeas=Traw1000×IratedI_{\text{meas}} = \frac{T_{\text{raw}}}{1000} \times I_{\text{rated}} M=Imeas×KtM = I_{\text{meas}} \times K_{t}

Combined:

M=(Traw1000×Irated)×Kt\boxed{M = \left(\dfrac{T_{\text{raw}}}{1000} \times I_{\text{rated}}\right) \times K_{t}}

2) When 0x8010:54 = FALSE (Peak current mode):
If the raw feedback represents peak current, convert peak → RMS (if you want an RMS-equivalent) by dividing by √2:

Imeas=Traw1000×Irated2I_{\text{meas}} = \frac{T_{\text{raw}}}{1000} \times \frac{I_{\text{rated}}}{\sqrt{2}} M=Imeas×KtM = I_{\text{meas}} \times K_{t}

Combined:

M=(Traw1000×Irated2)×Kt\boxed{M = \left(\dfrac{T_{\text{raw}}}{1000} \times \dfrac{I_{\text{rated}}}{\sqrt{2}}\right) \times K_{t}}

Numeric note: 2≈1.41421356\sqrt{2} \approx 1.41421356.

Unit flow / final unit

  • T_raw / 1000 is unitless (per-mille → fraction).

  • I_rated in A → I_meas in A.

  • K_t in Nm/A → M in Nm.

Quick implementation checklist

  • Confirm I_rated (0x8011:12) units in the drive (A).

  • Confirm K_t (0x8011:16) units (usually Nm/A) from motor/drive documentation.

  • Confirm whether T_raw is signed/unsigned and whether any scaling/offset is applied by the firmware.

  • Apply the appropriate formula depending on 0x8010:54.