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4.2.1
Analog Outputs
The YSI 2700 analyzer is capable of performing an analysis approximately every two minutes; it is
therefore incapable of producing a truly continuous signal which represents the instantaneous analyte
concentration. It is because of this "semi-continuous" nature of the instrument that the YSI 2730 interface
provides additional signals to aid in synchronizing the reading of the analog outputs. In addition to the two
analog outputs (one output per chemistry, black and white channels), two logical signals are provided.
These "handshake signals" are nom5 volts for a logic 1 and ground (0 volts) for a logic 0. The
"READY" signal is output from the YSI 2730 and is set to a logic 1 when the analog output signals have
been updated. This signal indicates to the host system that the analog voltages are "new" and that they
represent the most recent reading of the analyte concentrations. The host system (the external system to
which the YSI 2730 is connected) then can send a logic 0 to the "ACK" input of the YSI 2730. This
"ACK" (acknowledge) signal response from the host resets the READY line of the YSI 2730 to its low
state before the next sample is ready. Figure 8 shows the typical signal pattern that would occur during
two sample update cycles. The READY signal will reset itself immediately prior to updating the analog
outputs if not reset externally via the ACK\ signal input.
4.2.2
Pump Control Outputs
Three discrete outputs are provided on the YSI 2730 which are intended to control external pumps. The
means of control is on or off only, no intermediate states are supported. The three outputs are labeled
Black Channel Pump, White Channel Pump and Filtrate Pump. All of these outputs are electrically
identical and are designed as control signals only, i.e. they are incapable of driving any pumps directly.
These signals must be buffered externally in a manner appropriate to the nature of the pumps being used.
These output signals transition b5 volts and 0 volts nominally. The logic of each, i.e. whether 5
volts turns on or off the external device, is determined by the position of switch SW1 on the 2730 PC board
(See Section 3.2.3). Assuming no inversion enabled by the user, the output turns on the pump with a +5
voltage output, exclusive of any logic inversion imposed by the user supplied buffering circuitry.
A n a l o g O u t p u t
R e a d y
A c k \
Figure 8 Handshake Signals
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