L-Card L-502-P-G-D-I User Manual
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Contents
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46 Connection of signals.band up to 10 MHz are always present in the real situation, and also in the situation ofthe user's failure to apply a differential connection (and adjustment to the differentialmode), and therefore use the valuable property of a differential input – effectivelysuppressing common-mode interference.Physical cause #2. The high frequency of the 2 MHz channel switch (when tuned tomultichannel mode) with L-502 default settings may not only be a great advantage of the L-502ADC (in the high-speed ADC input interrogation), but it can also be a problem as it takes a shortsetting time for the measuring circuit (less than 500 ns after the switch's own charge is injected intothe measurement circuit). This cause is fundamental for all ADC with input commutator,manifested as a switching disturbance.4.5.2. Conditions for correct connection and settings L-502.1. If you need to use no more than 16 ADC channels, always select the differentialconnection mode and the L-502 settings.2. With a differential connection, the X and Y circuits of each channel always lead in pairs(twisted pair, shielded pair).3. The L-502 signal circuit must be shielded. On the screen connection, see 4.2.2.4. For differential connection, when using a pair cable, to maximize common-moderejection of the L-502, the output impedances from the remote source along the X and Ycircuits should be balanced, (connection example - p. 6.1.10).5. The AGND L-502 circuit must be connected to the common circuit of the signal source(if there are several signal sources to the common junction of the common signal sourcewires).6. If you need to configure the L-502 for multichannel operation, you first need to optimizethe signal-to-noise ratio of the ADC in a single-channel operation mode with amaximum data acquisition frequency of 2 MHz, in which in the signal spectrum you willsee all the frequencies of the interference (possibly from "mirror frequencies", ifinterference above 1 MHz), which means that you have a tool in your hands to find thesources and causes of these interferences (before going to multi-channel mode andaveraging mode, which will be much more difficult to understand with sources ofinterference).7. When using ("default") in the multi-channel operation mode of the maximumswitching frequency (2 MHz), the output impedance of the L-502 signal circuit mustbe from 0 to 50 Ω (in the frequency band up to 10 MHz), and this voltage sourcemust be linked to connector L-502 by wires of zero length. This is achieved either bydirectly connecting the output of the signal source itself (50 Ω) or by connecting its loadresistor (up to 50 Ω) directly to the cable part of the L-502 signal connector (whenconnecting an agreed 50-ohm line or a current shunt to 50 ohms of the external currentmeasurement circuit) .8. When using a multichannel mode of non-zero length of wires to the voltage sourceand (or) with an output resistance of the signal circuit of more than 50 ohms, theprogram setting of the signal conditioning time nsu > 1 (s. 3.3.6) should be applied. |
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