Hach 8450, Instrument Manual

Page: 42 / 66

Page 42
VMA Output Setup
16116Operation.fm
Section 3
3.17.6 Alarm Time Delays
The alarm time delay feature has been included for applications where
momentary swings in chlorine may occur but do not necessarily constitute an
alarm condition. A time delay from 0 to 600 seconds may be specified.
(Default value =10 seconds.)
3.18 VMA Output Setup
The residual chlorine monitor has two independent output channels. Each
channel has one voltage and one current signal output. The voltage signal
may be programmed for 0–1V or 0–5V output. The current output signal may
be programmed for normal 4-20 mA output or inverted 20-4 mA output for
operating inverse proportional pumps. In addition, outputs may be adjusted to
compensate for circuits that have higher current load demands (e.g., more
than one chart recorder) or for recording devices which may be slightly out-of-
calibration.
Each channel’s analog output signals are proportional to one of two readings
computed by the instrument: concentration (ppm) or temperature (°F or °C).
Figure 28 VMA (Analog Output Channels) Menu Screen
Unit —Sets the units which the channel’s volts/mA signals represent. The
selections are ppm, °F, and °C.
Spn —Sets the span in the selected units. Output signals are proportional
from 0.00 to the selected “Spn” value. Permissible values are: ppm,
1.00– 20.0 in 0.01 increments for values less than or equal to 9.99 and 0.1
increments for values greater than or equal to 10.
V —Sets the voltage range to either 0–1 V or 0–5 V.
mA —Set the 4-20 milliamp output to normal or inverted. The 4-20mA output
range may be inverted (20 mA=0.00, 4 mA=span) for operating inverse
proportional pumps.
On systems where more than one external recorder is connected to the same
analog output circuit, the output may require some adjustment to compensate
for circuit loading. Adjustment of VMA outputs is accomplished by entering the
“ADJ” menu and selecting the output channel and type. When selected, select
the icon and place the menu cursor on “Adjust” and select the icon. Use the
direction icons to increase (INC) or decrease (DEC) the output. Adjustment of
the output will require that either a volt/ammeter be connected to the output or
the recorder be visually available (see
Table 5 on page 32 ).
3.19 System Security
System security may be enabled to reduce the possibility of tampering with
system parameters. To enable system security, enter the “SEC” (security)
menu, select “ENABLE LOCK,” and enter a numeric password using the keys.
After enabling the system security and exiting the menu, the menu will display
“DISABLE LOCK.” Any attempt to change system operating parameters will
be met with a message to enter the security code. When the code has been
>Unit Spn V mA
PPM 20.0 | 0000