Datalink Option - GE Giraffe Service Manual

Chapter 1: Functional Description
The toroidal transformer is used to buck the mains voltage down to the range required for the elevating base
motor. The primaries mains input comes from the relay board and is switched by safety relay 2. The dual
primaries are connected in parallel for 115 volt operation and in series for 230 volt operation. The output
voltage from each secondary is about 15 volts for both 115 and 230 volt operation and is input to the relay
board motor control circuits.
The solid state relay (SSR) is used to switch the isolated 115 volts to the incubator heaters. The SSR is mounted
to the back wall of the electronics enclosure below the toroidal transformer.
The 8.4 NiMH battery is connected to the relay board. It is used to power the +5 STBY during power fail. The
battery charges only when the unit is powered on.

1.7 DataLink Option

The DataLink option allows direct output of serial data to various remote monitoring systems, such as a
computer or commercial RS-232 monitor. The DataLink option board contains the electronic circuitry necessary
to provide a 2500 VRMS isolated serial interface to meet the logic levels specified by EIA RS-232D and
CCITTV.28.
The MAX250 and MAX251 (U1 and U2), together with two 6N136 optocouplers and transformer TR1, form
an isolated RS-232 transmitter and receiver. The MAX250 connects to the non-isolated or "logic" side of the
interface, translating logic signals to and from the optocouplers, while the MAX251 resides on the isolated or
"cable" side, translating data between the optocouplers and RS-232 line drivers and receivers. In addition to
the optocoupler drivers and receivers, the MAX250 also contains isolation transformer drive circuitry which
supplies power to the isolated side of the interface, and the MAX251.
The transmit signal is input to the MAX250 driver (U1 pin 4) whose output (U1 pin 3) drives optocoupler U4.
The optocoupler output (U4 pin 6) is then fed into the MAX251 driver (U2 pin 3). The output of the MAX251
driver (U2 pin 12) is at the logic levels conforming to EIA RS-232D and CCITTV.28. Conversely, the receive signal
enters the MAX251 driver (U2 pin 10) and is stepped down to CMOS/TTL levels at U2 pin 5. This logic level drives
optoisolator input (U3 pin 3) whose output is fed into U1 pin 10. The output (U1 pin 9) signal is then available to
the control printed circuit board.
A slide switch SW1 is used as a "self test" for the RS-232 interface. In the closed position, the J30-1 transmit
signal is sent through the MAX250/MAX251 transmitter and back into the receiver portions. The signal can be
read at J30-2 and verified to be correct. Any external cable connection must be removed for this self test to
function. CR1 and CR2 provide transient protection for MAX251. In normal operation SW1 should be in the open
(OFF) position.
The nurse call signal is input at J30-5 as a TTL logic level. In the "no alarm" state, this signal is a logic high,
which turns on Darlington Q1, energizing relay K1. This results in contact closure between J31-1 and J31-2.
In the "alarm" state, J30-5 is a logic low, which turns off Q1, de-energizes K1 and results in contact closure
between J31-2 and J31-3. K1 provides 2500 VRMS isolation between the relay coil inputs and contact outputs.
6 © 2001 by Datex-Ohmeda, Inc.. All rights reserved.
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