Data accumulation rate

This page gives some rules for estimating the accumulation rate of data on disk for a running MCE.

Rate calculations

In general, during a regular acquisition, the data rate (bit rate) of an MCE is:

<math>S_w \times (S_{head} + N_c \times N_{RC} \times N_{rro} + S_{chk}) \times f_{DV}</math>

where:

• <math>S_w</math> is the word size (=32 bits)
• <math>S_{head}</math> is the size (in words) of the frame header (=43 words)
• <math>N_c</math> is the number of columns per readout card (=8)
• <math>N_{RC}</math> is the number of readout cards read out (see rcs_to_report_data)
• <math>N_{rro}</math> is the number of rows read out (i.e. num_rows_reported)
• <math>S_{chk}</math> is the size (in words) of the frame checksum (=1 word)

<math>f_{DV}</math> is the read-out data rate. When in internal-DV mode (i.e. use_dv is zero), this is:

<math>f_{DV} = \frac{50\;\mathrm{MHz}}{ N_{dr} \times N_{r} \times N_{rl} } \equiv \frac{f_{ARZ}}{N_{dr}}</math>

where:

• <math>50\;\mathrm{MHz}</math> is the clock rate
• <math>N_{dr}</math> is the number of samples co-added into an output frame (i.e. data_rate)
• <math>N_{r}</math> is the number of rows servoed (i.e. num_rows)
• <math>N_{rl}</math> is the row dwell-time in clock periods (i.e. row_len)

and

• <math>f_{ARZ}</math> is the Address-return-to-zero rate, i.e. the frequency at which a single pixel is visited

A useful approximation is:

a single readout card reading 41 rows at 400 Hz is <math>\approx0.5</math> megabytes/second.

Tables

Here are some tables of accumulation rates for both kinds of subracks for various data rates and numbers of rows:

MCE data accumulation rate in Megabits per second (Mbps)

	48HP					72HP
	100 Hz	150 Hz	200 Hz	400 Hz		100 Hz	150 Hz	200 Hz	400 Hz
25 rows	1.28	1.92	2.56	5.12		2.56	3.84	5.12	10.24
33 rows	1.69	2.53	3.38	6.76		3.38	5.07	6.76	13.52
41 rows	0.94	1.42	1.89	3.78		1.42	2.83	3.78	7.56

MCE data accumulation rate in Gigabytes (10⁹ bytes) per hour

	48HP					72HP
	100 Hz	150 Hz	200 Hz	400 Hz		100 Hz	150 Hz	200 Hz	400 Hz
25 rows	0.58	0.86	1.15	2.30		1.15	1.73	2.30	4.61
33 rows	0.76	1.14	1.52	3.04		1.52	2.28	3.04	6.08
41 rows	2.10	3.15	4.20	8.40		4.20	6.30	8.40	16.79

MCE data accumulation rate in Gigabytes (10⁹ bytes) per day

	48HP					72HP
	100 Hz	150 Hz	200 Hz	400 Hz		100 Hz	150 Hz	200 Hz	400 Hz
25 rows	13.8	20.7	27.7	55.3		27.7	41.5	55.3	110.6
33 rows	18.1	27.4	36.5	73.0		36.5	54.7	73.0	146.0
41 rows	22.7	34.0	45.3	90.7		45.3	68.0	90.7	181.4