SL900A datasheet(22/103 Pages) AMSCO

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[v1-12] 2018-Oct-29

SL900A − System Description

Logging Timer

The SL900A device has an integrated RC oscillator that is

calibrated to 1024Hz. This oscillator drives the logging timer.

The logging timer resolution is 1 second. The maximum period

is 9.1 hours (32768 seconds). The logging interval is

programmed with the SET LOG MODE command.

The measurement real time is derived from 4 parameters - the

Start time (ST ), the Delay time (DT ), the log interval (LT), and

the # of the measurement (NM). This value has to be calculated

in the reader by the equation:

Real time = ST+DT+LT*NM

Delay Time

The SL900A supports delayed start of the logging procedure.

The Delay time has a resolution of 8 minutes - 32 seconds (512

seconds) and a maximum value of 582 hours (12 bits). The delay

time value is set with the Initialize command, while the Delay

time counter starts counting when the device receives the

START LOG command.

The delay time can also be disabled and an external push button

can be used for starting the logging procedure.

Analog to Digital Conversion

The chip has an integrated analog to digital converter with

10-bit resolution and selectable voltage references. By default,

the references are selected as: Vo1 = 260mV and Vo2 = 410mV.

Input voltages between Vo2 and 2xVo2-Vo1 are converted into

a 10-bit ADC value.This results in a nominal voltage input range

of 410mV ~ 560mV, for the temperature conversion this is

nominally -29.3ºC ~ 58.1ºC.

The ADC voltage references are individually selectable in 50mV

steps with a fine adjustment for offset calibration. Additionally,

the Vo1 reference voltage can be tied directly to ground if the

bit “gnd_switch” in the SET CALIBRATION DATA command is set

to 1 (SPI address 0x012). Please note if Vo2 and/or Vo1 are

changed from their default values the calibration of the

temperature sensor is no longer valid.

(EQ1)

SL900A Datasheet(PDF) 22 Page - ams AG