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Sensors Signals Timing


Each sensor has different timing.
The real timing depends on multiple parameters:
  • Exposure Time (ET). This time is defined by xiAPI by (XI_PRM_EXPOSURE)
  • Data Readout Time (t rd). It depends on:
    • Sensor bit depth
    • Binning or Skipping selected
    • Region of Interest (ROI) used
    • Sensor clock which depends on Transfer speed (MB/s)
    • Amount of data transferred (MB) - depends on image resolution and number of bits transferred per pixel (BPP)
    • Channel count used for data read out

Calculators

In order to simplify calculation of frame-rate or other parameters - use one of the following calculators based on camera sensor type:

Free-Run mode (no trigger)

Each image exposition is started automatically when possible. This mode gives the highest fps (frames per second) that is possible on the sensor.

Exposure Overlapped with Data Readout Mode

This Overlapped mode gives the highest number of frames per second.


Sensor timing in Exposure Overlapped with Data Readout Mode


In this mode the timing depends on minimum of Exposure Time and Data Readout Time.

Triggered mode without overlap

Each image exposition is triggered with input trigger signal.
This mode gives lower fps value compared to Free-Run mode.

Exposure Not Overlapped with Data Readout Mode

Most sensors uses this mode when input trigger is active.
This mode gives lower fps value than Exposure Overlapped with Data Readout mode.


Sensor timing in Exposure Not Overlapped with Data Readout Mode


In this mode the timing depends on sum of:
  • Input transition time (t itr) depends on:
    • Digital Input Delay - time for changing internal circuit to active state. It is constant for each camera model.
    • Input Debouncing Time - time for stabilizing uneven input signals (e.g. from mechanical switches). This time can be can be set using xiAPI with parameters XI_PRM_DEBOUNCE_EN and XI_PRM_DEBOUNCE_T0 on some cameras. Default 0.
  • Exposure time (see ET above).
  • Data Readout time (see t rd above)


Table1: Typical times for selected camera models

Camera Model DownS t itr [µs] t exp [µs] t eio[µs] t expo[µs] t rd[µs] Notes
MU9 models:
MU9 any 200+
xiQ/MQ models:
MQ013xG-E2 any 1.4 29 19/238 10 400+16.4*BWF*LC N1, N2
CURRERA-R - OC models:
RL13-OC any 0.1 42 18 0 400+16.4*LC
RL50-OC 1 0.1 2 0.3 0 2000+37.7*LC
RL50-OC 2 0.1 2 0.3 0 2000+32.4*LC
RL50-OC 4 0.1 2 0.3 0 2000+46.1*LC
RL04-OC 1 0.1 11 11 0 1500+36.8*LC
RL04-OC 2 0.1 11 11 0 800+35.8*LC
RL04-OC 4 0.1 11 11 0 680+40.1*LC
CURRERA-R - 24V models:
RL13-24 any 0.1 109/18 127/36 0 400+16.4*LC
RL50-24 1 0.1 109/18 109/18 0 2000+37.7*LC
RL04-24 1 0.1 109/18 127/36 0 1500+36.8*LC

Note N1: V(Input)=15V
Note N2: x in model name means all available models (M, C, R)

Table1 column names:
DownS = Current camera DownSampling (XI_PRM_DOWNSAMPLING)
t eio = Trigger (Digital Input) to Strobe (Digital Output) (on some models is listed: Off->On change / On->Off change)
t exp = Strobe (Sensor) to Digital Output (on some models is listed: Off->On change / On->Off change)
t expo = Start of exposition to Exposure Active Digital Output
LC = Current Line Count (XI_PRM_ HEIGHT)
BWF = Bandwidth Factor for maximum bandwith this is 1 when the bandwith will be lower BWF will rise (TBD)
t exps = Current Exposure Time set (XI_PRM_EXPOSURE)
Conditions: XI_PRM_DEBOUNCE_EN=0 (off).

Minimum trigger period (Ttrig_min)

Minimum trigger period can be calculated using the following formula:
  • t trig_min = t exp + t exps + t rd

Example for MQ013MG-E2, Exposure time = 500us, image = 500 pixels width x 200 pixels height.
  • t trig_min = 29µs + 500µs + 400µs + 16.6µs * 200lines = 4249µs

Triggered mode with overlap

Several sensors are capable to trigger exposure in overlap mode, so it is capable to reach the same fps value as in free run mode.

When trigger period is longer than exposure and readout the signal wave form will look similar to Trigger mode without overlap.

However, when the trigger period will decrease sensor will expose images in overlap mode.
In this case frame active signal will be all the time active.


Sensor timing in Exposure Overlapped with Data Readout Mode

The maximum FPS can be calculated using FPS_calculator_CMV.xlsx .


For timing description please see previous paragraph Triggered mode without overlap

Table2: Typical times for selected camera models

Camera Model DownS t itr [µs] t exp [µs] t eio[µs] t expo[µs] t rd[µs] t fot[µs] Notes
xiQ models:
MQ042xG-CM any 1.4 10 11/224 0 (64.5+5.375*LC)*BWF 64.5 N1,N2
MQ022xG-CM any 1.4 10 11/224 0 (37.625+5.375*LC)*BWF 37.625 N1,N2
MQ003xG-CM any 1.4 10 11/224 N3 0 (92.8 + 3.78 * LC)*BWF 92.8 N1,N2
MQ013xG-ON any 1.4 <2 11/224 0 (23*W+3300)/BW+(7.66*W+1106)*LC/BW N1,N2

Note N1: V(Input)=15V
Note N2: 8bit per pixel maximum bandwidth (TBD)
Note N3: Exposure is delayed for short exposure times. If (t exps < t rd) then t eio = t eio + (t rd-t exp) approx.
Conditions: XI_PRM_DEBOUNCE_EN=0 (off).

Table2 legend:

DownS = Current camera DownSampling (XI_PRM_DOWNSAMPLING)
t eio = Trigger (Digital Input) to Strobe (Digital Output) (on some models is listed: Off->On change / On->Off change)
t exp = Strobe (Sensor) to Digital Output (on some models is listed: Off->On change / On->Off change)
t expo = Start of exposition to Exposure Active Digital Output
t exps = Current Exposure Time set (XI_PRM_EXPOSURE)
W = Image width(XI_PRM_WIDTH)
LC = Current Line Count (XI_PRM_ HEIGHT)
BW = Bandwidth in Mbit/s
BWF = Bandwidth Factor see table below

Bandwidth factor

Bandwidth factor is a number reflecting the ratio between the maximum pixel clock frequency and the current pixel clock frequency calculated from the Bandwidth Limit.
 
BWF = F max / F limit
 
Where F max is the maximum possible pixel clock frequency for the given sensor (in MHz) and F limit is the current pixel clock frequency which depends on the bandwidth limit parameter set in the API (XI_PRM_LIMIT_BANDWIDTH). F limit is set in 1MHz steps and can not go lower than F min.

Table3: pixel clock info

Camera Model F max [MHz] F min [MHz] F limit [MHz]
MQ042xG-CM
MQ022xG-CM
48 5 ((129*BWL)/(1024*BPP))*((12+LC)/LC)*(W max/W)
MQ042xG-CM SR2
MQ022xG-CM SR2
48 20 ((129*BWL)/(1024*BPP))*((12+LC)/LC)*(W max/W)
MQ003xG-CM 43 38 ((325*BWL*)/(316224*BPP))*(13+LC/2)*(W max/W)

Table3 legend:
BPP - number of bits per pixel of the transport pixel format
BWL - currently set bandwidth limit in Mbit/s
W - image width
W max - maximum possible image width

Minimum trigger period (t trig_min )

Minimum trigger period can be calculated using the following formula:
  • t trig_min = t exp + t exps (When exposure time is longer than readout time)
  • t trig_min = t rd (When exposure time is significantly shorter then readout time)
  • t trig_min = t exps + t fot (When exposure is smaller than readout time but the difference is less than t fot )
Example for MQ022xG-CM, Exposure time = 500us, image = 2048 pixels width x 1088 pixels height with maximum bandwidth and 1 byte per pixel.
  • t trig_min = 10µs + (37.625+5.375*1088lines) * 1 = 5895µs