Frequently Asked Questions

Answers to Commonly Asked Questions about Liberty* MDrive with Multi-turn Absolute Encoder.

Home > All ProductsAbsolute MDrive > Frequently Asked Questions

Frequently Asked Questions

What is the encoder resolution of Absolute MDrive?

The Absolute MDrive has the same encoder resolution as the existing closed-loop Liberty MDrive products, 1000 lines or 4000 counts/revolution.

Is the encoder resolution actually 4000 or 4096 counts/rev?

The resolution is actually 4000 counts/revolution. The analog input resolution for the Liberty MDrive is 4096, but the analog input is not available on the Absolute MDrive.

How many shaft rotations may occur before the multi-turn encoder loses position due to counter over-run?


Motion Control, Ethernet TCP/IP

To prevent rollover of Idx6062h (Position_demand_counter) an automatic rollback feature has been incorporated. When this counter reaches or exceeds 7/8 of the way (i.e. 70000000h=1,879,048,192), the counter is rolled back by that value. This is done to avoid confusing the internal micro-stepper state machine from interpreting a very positive number (i.e., >2^31) as a negative number and prevents the software routines from doing the same. Please note that a roll back feature is not available on the encoder itself. As a result, if Idx6064h (Position) is based on the encoder, Idx6064h (Actual) value will be offset from Idx6062h (Demand), and a following error will be set.The encoder counter (C2) is a 32-bit register, meaning the shaft can rotate approximately +/- 41,000 revolutions before losing position.

How long will Absolute MDrives retain position information?

The unit will retain its position information for up to 30 days without the use of the optional ICP0531 External Battery Pack.

How many Absolute MDrives can the Battery Pack provide power to?

The optional ICP0531 External Battery Pack provides power to up to six (6) Absolute MDrives.

How long will the optional ICP0531 External Battery Pack allow Absolute MDrive position to be retained?

Using the optional ICP0531 External Battery Pack with six (6) Absolute MDrives connected, position will be retained for up to five (5) years. It is recommended that power be supplied to the Absolute MDrive for a minimum of twenty-four hours prior to changing batteries or disconnecting the optional ICP0531 External Battery Pack.

Are low level warning provisions available on the optional ICP0531 External Battery Pack?

  1. Yes, the optional ICP0531 External Battery Pack is equipped with a status LED. The LED will flash on every 10 seconds while the internal battery voltage is above the required threshold. If the status LED is not flashing, the internal battery voltage is not sufficient, and internal batteries will need to be replaced.

  2. The optional ICP0531 External Battery Pack is also equipped with a low battery signal output. The low battery signal output is essentially an open collector. When internal battery voltage is insufficient, the low battery signal output will provide 24 VDC. Internally, we utilize a 5.62K ohm resistor to pull up to 24 VDC. Current is based on the impedance of the input or load.

What are the environmental condition limits for the optional ICP0531 External Battery Pack?

The environment during transport and storage must be dry and free from dust. The maximum vibration and shock load must be within the specified limits for the Absolute MDrive.
Temperature (°C)-25 to 70
Temperature variation (°C)-25 to 30
Humidity (%)5 to 95 (non-condensing)
Note: Environmental conditions listed are only applicable to the ICP0531 External Battery Pack. Upon installation of batteries, manufacturer environmental condition limits for batteries must also be considered.

What is the Absolute MDrive encoder communication protocol, SSI or EnDAT?

The Absolute MDrive encoder utilizes communication technology proprietary to SEM. The absolute encoder does not utilize SSI or EnDAT communication protocols.

Can Programmable Motion or Ethernet TCP/IP Absolute MDrives provide position via encoder output signals?

Due to hardware restrictions, it is not possible for the Absolute MDrive to provide position information via encoder output signals. Position information is available by querying the encoder counter (PR C2 or fieldbus equivalent).

Why do I receive error 121?

Error 121 is defined as absolute encoder communication failure.
Typical causes for this error are as follows:
  1. An unrecoverable event, such as high internal impedance across absolute encoder circuitry, has resulted in a large voltage spike which has damaged the device.
  2. Battery backup voltage has been exceeded and damage has occurred on the device. The maximum allowable backup voltage is 6VDC.

Why do I receive error 122?

Error 122 is defined as absolute encoder was reset and position was lost.
Typical causes for this error are as follows:
  1. Device counters have been reset. If absolute encoder circuitry voltage drops below 3.2 VDC and external battery is below 3.5 VDC, C1, C2, and P counters are reset.
  2. Position discrepancy due to loss of synchronization. Writing to various counters during operation can cause a loss of synchronization. This error may appear after the synchronization event, such as a power cycle.

Why do I receive error 123?

Error 123 is defined as unable to compute new absolute encoder count. Bad data has been received from internal absolute encoder circuitry.
Possible causes:
  • hold up time exceeded without the use of the optional external battery pack
  • overheating
  • encoder wheel misalignment
Novanta IMS