Teledyne 4250 Installation And Operation Manual page 46

4250 Flow Meter
Section 2 Programming
2-18
condition (or set of conditions) that must occur before the
sampler is enabled. You enter a value (level is an example) that
must be met before the enabling occurs.
But what if this value is met and then falls away? It is possible
for a condition to vary rapidly over a narrow range. Without hys-
teresis, the flow meter will turn the sampler off and on
repeatedly, causing a condition known as chattering, that would
result in very erratic operation of the sampler.
With hysteresis, you can enter a value that will keep the flow
meter from responding to insignificant changes in the enabling
condition. You should select a value for hysteresis that is narrow
enough to allow the flow meter to respond to any serious change,
but broad enough to ignore minor changes that could cause chat-
tering. Press Enter and the following will appear:
VELOCITY ENABLE/ALARM
HYSTERESIS XX.XXX FT/S (or meters/second)
Press Enter again and the following will appear:
FLOW RATE ENABLE/ALARM
HYSTERESIS XX.XXX CFS (or other units of measure)
The next three menus may or may not appear, depending on
o t h e r s e l e c t i o n s y o u m a k e i n P r o g r a m . T h e y c o n c e r n
alarm/enable hysteresis set points for parameter sensing—tem-
perature, pH, D.O., and the YSI 600 Sonde outputs.
If you want to set hysteresis for any of these items, you should
enable them when you work through the program section, then
re-enter the Setup section (Hysteresis) and they will appear.
Note that you can have temperature alone, or temperature with
either pH or D.O., but you must have temperature with either
pH or D.O.
Note
You cannot have pH and D.O. at the same time, and selection
of one will prevent the other from appearing on the menus
later.
The following will appear if you are measuring temperature:
TEMPERATURE ENABLE/ALARM
HYSTERESIS XX.XXX DEG F (or C)
The following will appear if you are measuring pH:
pH ENABLE/ALARM
HYSTERESIS X.XXX pH
The following will appear if you are measuring D. O:
DO ENABLE/ALARM
HYSTERESIS X.XXX PPM
(or mg/l depending on units selected in Program.)