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8
Getting Started with DT800
dataTaker
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Look, No Hands
Once you’ve set the DT800 running you can
disconnect the computer if you wish — the DT800
continues to operate as programmed because the
software which controls the logger is inside the logger
itself. This is called
stand-alone
operation.
Input Types
The DT800 lets you monitor, record and raise alarms
for readings from many types of sensors and
transducers — temperature (thermocouples,
thermistors, RTDs and solid-state sensors), pressure,
flow, strain, digital state (high or low, off or on), count,
frequency, period, voltage, current, resistance and so
on.
You can connect many sensors — each one different
— to a single DT800 and have them scanned
whenever you choose.
Meaningful Quantities
Whatever the sensor, its raw output will be either
voltage, current, resistance, frequency, time, counts or
digital state. For example, the output from a
thermocouple is a voltage that varies according to the
temperature being measured: the thermocouple’s raw
output is volts (under 100 millivolts, actually), not
degrees Centigrade or Fahrenheit.
Then the raw output must be converted to a meaningful
quantity (to a temperature value in this example).
Depending on the type of sensor, this conversion
involves
linearization
and possibly
compensation
,
terms which are beyond the scope of this guide. Just
be aware that raw measurements usually have to be
converted before they become the meaningful
quantities that are useful to you (Figure 3).
One of the features of the DT800 is that it
automatically performs these conversions for you. All
you have to do is tell the logger what
type
the sensor is
(a type T thermocouple, for example) and the
microprocessor inside the logger performs the
appropriate linearization and compensation, turning
the raw sensor output into a quantity with meaningful
units.
The DT800 measures these fundamental
parameters, from which all others are derived:
voltage
resistance
frequency
time
counts (pulses)
thermocouple reference temperature
Sending Commands
There are three ways you can send commands to
the DT800:
• from a computer connected to the DT800
• from a removable memory card — commands
loaded into a memory card can be transferred to
the DT800 and acted upon the moment the card is
inserted into the DT800’s memory card socket (this
is a handy way of configuring and programming
a remote DT800)
• using alarms (see the
DT800 dataTaker User’s
Manual).
This means that the DT800 supports many types of
inputs. For example:
voltage
resistance
current (including 4–20mA loops)
thermocouples
thermistors
RTDs (Resistance Temperature Detectors)
solid-state temperature sensors
bridges (strain gauges)
frequency
time
counts
pressure sensors
flow sensors
load cells
digital state (on/off, high/low)
Содержание DT800
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