7.1.9 Transfer Delay with Digital Scanners

Transfer Delays are inherent in systems where the SP-ICE-3 Card is used to control digital scanners.

Transfer Delays in Detail

Transfer Delay (TX)

The time which elapses between the SP-ICE-3 Card sending a position command to the scanner, and its being recognised by the controller algorithm in the scanner.

It is dependent on the Interpolation Time set in the scanner.

Transfer Delay (RX)

The time which elapses between the scanner controller sending a measured position, and that measured position being received by the SP-ICE-3 Card.

(No Transfer Delay)

Laser control signals are sent from the card directly to the laser with practically no delay.

Note
Transfer Delays are not dependent on the Tuning of the scanning system, but the selected Tuning may well affect the scanner's Tracking Error value. The card emits position commands synchronously with the laser signals, but the laser and the scanners, by their very nature, do not react to the signals simultaneously. Consequently, you should set LaserOnDelay and LaserOffDelay to values that take the scanner's total Positioning Delay into account, i.e. the sum of Transfer Delay and Tracking Error (a.k.a Lag).

Note

Transfer Delays are not dependent on the Tuning of the scanning system, but the selected Tuning may well affect the scanner's Tracking Error value.
The card emits position commands synchronously with the laser signals, but the laser and the scanners, by their very nature, do not react to the signals simultaneously.
Consequently, you should set LaserOnDelay and LaserOffDelay to values that take the scanner's total Positioning Delay into account, i.e. the sum of Transfer Delay and Tracking Error (a.k.a Lag).

Calculation of Transfer Delays

Important

The information in this section applies only to recent firmware versions:

Scanner Firmware - Dicon2.5
FW v6973 onwards
FPGA v6921 onwards
SP-ICE-3 Firmware
v2.0.2 onwards

Transfer Delay (TX)

TD_TX can be approximated (to ±2us) as follows:

Interpolation Time
Transfer Delay (TX)
T_Int > 0
TD_TX = T_K + T_C + T_Int
T_Int = 0
TD_TX = 14 µs

Where:

Factor

Value

Description

Notes

T_K

13 µs

Constant delay factor for Interpolation Time > 0.

See Note below.

T_C

20 µs

Calculation time of the interpolation routine.

Fixed quantity.

T_Int

t µs

Interpolation Time setting.

Note that an Interpolation Time setting of less than 20μs is not generally useful, due to the scanner controller's interpolation algorithm.

For the SP-ICE-3 Card, the Interpolation Time should normally be set to a small, non-zero multiple of twice the step period, e.g. 20μs.

Transfer Delay (RX)

TD_RX may be assumed to be constant, and independent of the scanner's Interpolation Time.

Transfer Delay (RX)
TD_RX = 36µs

Querying Transfer Delays via the Enhanced Protocol

Important

The information in this section applies only to recent firmware versions:

Scanner Firmware - Dicon2.5
FW v6973 onwards
FPGA v6921 onwards

Application software can retrieve current Transfer Delay values for digital scanners by using the appropriate Enhanced Protocol commands.

Delay Value	Enhanced Protocol Raw Command
Transfer Delay (TX)	0x0556
Transfer Delay (TX) + Transfer Delay (RX)	0x0557