Preamp Set-Up and Filtering Description

Pulses at TP17
Pulses Duration At TP6 (MS)
Result on Preamp Setup

1

64

Not Used

2

128

Not Used

3

192

Not Used

4

256

Lead III

5

320

Lead II

6

384

Lead I

7

448

Std

8

512

Lead III + Cal

9

576

Lead II + Cal

10

640

Lead I + Cal

11

704

Std + Cal

12

768

Lead III + Leads coil Drive and Switch Smooth

13

832

Lead II + Leads coil Drive and Switch Smooth

14

896

Lead I + Leads coil Drive and Switch Smooth

15

960

Std + Leads coil Drive and Switch Smooth

16

1024

Lead III + Cal + Leads Coil Drive and Switch Smooth

17

1088

Lead II + Cal + Leads Coil Drive and Switch Smooth

18

1152

Lead I + Cal + Leads Coil Drive and Switch Smooth

19

1216

Std + Cal + Leads Coil Drive and Switch Smooth

20

1280

Lead III + Paddles Coil Drive and Switch Smooth

21

1344

Not Used

22

1408

Not Used

The +1mV calibration signal is created by an instruction from the System microprocessor which sets U33 pin 7 high. When U43A closes, a -5V offset signal is applied to U44A pin 2 and U44B pin 6. This adds a differential offset of approximately +ImV to the input without changing the gain of the input stages.

Filtering.

Filtering provides a uniform signal bandwidth during normal operation. The preamp filtering is performed by two stages centered around op amps U44C, U45D, U45A, and U45B. In the first stage, U44C and U45D function as a high-pass filter for Preamp, DC Restore, and switch smoothing, blocking frequencies below 0.024Hz. In the second stage, low-pass filter U45A removes frequencies above 200Hz. U45B functions as a 540Hz notch filter.

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