Welch Allyn SureTemp 670 Especificaciones descargar pdf (Pagina 31)

Theory of Operation

SureTemp

Model 678/SureTemp

Model 679 4-9

Probe Switch

When the probe has been inserted in the probe holder, the probe switch (S4) brings

PROBE SW (U1-15) high (VCC). When the probe is removed from the probe holder,

the probe switch brings PROBE SW (U1-15) low (GND). R6 (47K) allows the probe

switch to be overridden by the test port.

Mode Button

The mode button (S2) is a momentary contact switch. A pullup internal to the

microprocessor normally pulls /MODE (U1-25) high, placing a logic “1” at this input.

When depressed, S2 provides a momentary contact to ground at /MODE giving it a

logic level of “0”. The software continuously checks /MODE. If the thermometer is not

in the process of taking a temperature, pressing the Mode button will wake up the

thermometer and display the last recorded temperature.

Timer Button (678 Only)

The timer button (S1) is also a momentary contact switch. A pullup internal to the

microprocessor normally pulls /PTIMER (U1-26) high, placing a logic “1” at this input.

When depressed, S1 provides a momentary contact to ground at /PTIMER giving it a

logic level of “0”. The software continuously checks /PTIMER.

Serial Communications Port

Transmit , receive data and control CMOS-level signals are made available for test or

system integration via J4. The contacts of J4 are laid out so they are accessible

through a slot in the rear of the case. Communications on a cable length of over one

foot should be driven with external RS232 or other line driving circuitry.

Horn

The horn is activated at the start of a temperature taking cycle, at the end of a Normal

mode temperature cycle, during timer operation at 0, 15, 30, 45 and 60 seconds, and

for various error conditions.

•

A short duration single beep is indicative of normal operation.

•

A short duration double beep is used to indicate errors and warnings such as

switching from Normal mode to Monitor mode during a temperature cycle.

The horn is a piezoelectric ceramic resonator driven by the processor square wave.

The horn control signal comes from U1 pin 49. It directly drives the horn LS1.

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 48 49

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Welch Allyn SureTemp 670 Especificaciones Pagina 31