Filter (conversion times)

The EL331x terminals are equipped with the following digital filters, cf. the data flow in chapter Data processing

Filter 1: in ADC, "ADC filter"

in all EL331x
setting in CoE 0x80n0:15
the higher the filter frequency, the faster the conversion time.
always have notch filter behavior (average filter)
the filter frequencies are set for all channels of the EL331x terminals centrally via index 0x8000:15 (channel 1). The corresponding higher channel indices 0x8010:15, 0x8020:15, 0x8030:15 etc. of the EL3312/EL3314/EL3318 have no function
"Enable Filter" in CoE 0x80n0:06 has no function, the ADC filter is always active

Filter 2: in firmware, “MC Filter (software filter in the microcontroller (MC)”

Only for EL3314-0002, EL3314-0092, EL3314-0010/0020/0030
Setting in CoE 0x80n0:1A: inactiv/IIR/FIR

Filter behavior

Example IIR low-pass 100 Hz:

Filter (conversion times) 1: — Example IIR low-pass 100Hz

The notch filters attenuate the designated frequency and multiples thereof, here using the example 50 Hz FIR,
Typical curve of a notch filter set to 50 Hz:

Filter (conversion times) 2: — Example notch filter

Conversion time/update rate from filter 1 (ADC filter)

The conversion time is dependent on the following:
Active channels * Number of measurements * Filter period + Calculation time = Conversion time

Example: EL3311 (1 channel), 3 measurements (thermocouple, wire break, cold junction), filter 50 Hz

1 channel * 3 measurements * (1/50 Hz) + 3 ms ≈ 63 ms

Example: EL3314 (2 channels), 3 measurements (thermocouple, wire break, cold junction), filter 50 Hz

2 channels * 3 measurements * (1/50 Hz) + 6 ms ≈ 126 ms

Example: EL3314 (4 channels), 3 measurements (thermocouple, wire break, cold junction), filter 50 Hz

4 channels * 3 measurements * (1/50 Hz) + 12 ms ≈ 252 ms

Typical conversion times with 3 measurements (thermocouple, wire break, cold junction)

Conversion times in relation to the filter frequencies:

	Conversion time (update time)
Filter frequency	EL3311	EL3312	EL3314	EL3314-0010 EL3314-0020 EL3314-0030	EL3318
5 Hz	0.6 s	1.2 s	2.4 s	1.6 s	3.5 s
10 Hz	0.3 s	0.6 s	1.2 s	800 ms	1.75 s
50 Hz	63 ms	126 ms	250 ms	165 ms	380 ms
60 Hz	53 ms	106 ms	210 ms	145 ms	320 ms
100 Hz	33 ms	66 ms	130 ms	86 ms	200 ms
500 Hz	9 ms	18 ms	33 ms	26 ms	70 ms
1000 Hz	6 ms	12 ms	24 ms	18 ms	50 ms
2000 Hz	5 ms	10 ms	20 ms (14 from FW10)	14 ms	40 ms
3750 Hz	4 ms	8 ms	19 ms (12 from FW10)	12 ms	35 ms
7500 Hz	4 ms	7 ms	19 ms (10 from FW10)	12 ms	30 ms
15000 Hz	3 ms	7 ms	19 ms (9 from FW10)	12 ms	30 ms
30000 Hz	3 ms	7 ms	19 ms (8 from FW10)	12 ms	30 ms
mV range	3 ms	6 ms	12 ms	12 ms	25 ms

Conversion times in relation to the filter frequencies, EL3314-0002 (from FW02), EL3314-0092:

Filter frequency	EL3314-0002, EL3314-0092
50/60 Hz	114 ms
2.5 Hz	2400 ms
5 Hz	1200 ms
10 Hz	600 ms
16.6 Hz	360 ms
20 Hz	300 ms
50 Hz	122 ms
60 Hz	102 ms
100 Hz	62 ms
200 Hz	31 ms
400 Hz	17 ms
800 Hz	10 ms
1000 Hz	8 ms
2000 Hz	5 ms
4000 Hz	4 ms
mV range	4 ms

Conversion time from filter 2 (MC filter)

If available, the MC filter can further attenuate the temperature value. The final conversion rate results from the conversion time set in the ADC (table in previous section) and the MC setting according to

F_{Filter frequency final} [Hz] = 1 / (k * t_{conversion time ADC})

with k as measure for the signal rise up to 70% (-3 dB) after

Filter designation	k	Behavior
FIR4	3	Notch filter behavior
FIR8	6
FIR16	12
FIR32	23
IIR0	2	Low-pass behavior
IIR1	5
IIR2	10
IIR3	19

Example: for the EL3314-0010 with ADC filter 50 Hz (thus 166 ms according to the above table) and FIR16 results in F_{Filter frequency final} = 1 / (12 * 166 ms) = 0.5 Hz.