Liquid Controls SP2800 - Manual (Page 37)

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5-1.2 Internal Buffer for Frequency Output
An internal buffer will store up to 9,999 counts if
the scaled input generates pulses faster than
the output speed selected. The warning mes-
sage "DATALOST" flashes on the screen when
the buffer overflows (see Section 6-1, Warning
Messages). This indicates that the counts being
totalled and the scaled outputs may be incor-
rect.
Note: All counts stored in the internal buffer will
be pulsed out at the selected frequency
even if the counter is reset before it is
finished sending them.
Figure 5-0.1
5-2 Control Outputs
5-2.1 SPDT Relay Version (Standard)
When the start button is pushed, the two relays
engage simultaneously to start flow. When the
prewarn number is reached, one relay drops
out. When the preset number is reached, the
other relay drops out. The user may enter the
two numbers when setting up the batch counter
(see Section 3-3, Menu Items 1 and 2). The
contacts are rated at 10 A, 120/240 VAC or 28
VDC.
5-2.2 Open Collector Version (Terminal 19,
20).
The NPN, Open Collector Transistors, sink a
maximum of 250 mA at 30 VDC when active.
They behave in the same manner as the Re-
lay Outputs (see Section 5-2.1 above). The
Open Collector outputs are available on units
with relay outputs, but, please observe the fol-
lowing precautions.
Note: When relays are used, 10 VDC is pro-
vided at the transistor outputs through
the relay coils. If current greater than
2 mA is drawn, the relay will remain
energized. Applying greater than 10
VDC to the Open Collector outputs
may destroy the unit. The transis-
tor will sink 100 mA in the "ON"
state with relays installed.
5-3 Optional Analog Output (Terminal 3)
5-3.1 Electrical Characteristics of Analog
Output
The Analog Output option is not available on
units with Square Law inputs. Controlled by
an Open Collector transistor, it gives a linear
4 to 20 (or 0 to 20) mA sink which corre-
sponds to displayed rate or total readings. A
sinking driver pulls a current to ground, across
the user's external device (such as a strip
chart recorder, computer, external meter, etc).
In the Setup mode the user is prompted to set
the output to correspond to rate or total and
set the low and high (4/0 to 20mA) parame-
ters to which the analog signal will corre-
spond.
Idea: The Batcher can supply the 24VDC to
power the current loop. (Connect pin
15 to 13, Pin 16 is now +24 VDC with
respect to pin 12.) Connect Pin 16 to
the + DC side of the external device
and connect Pin 3 to -DC side of the
external device (see Figure 5-2.1).