Early Burn-Out Detection; Pulse Output - Eaton CROUSE-HINDS Series Instruction Manual

Output current
22.250mA
20mA
4mA
3.8mA
Range
begin

10 .4 Early Burn-out Detection

This feature is an aid to anticipate the failure of thermocouple sensors. With age and
exposure to temperature cycling the junction of the two dissimilar thermocouple
materials starts to break down and eventually becomes an open circuit. This is
commonly known as "burnout" of the sensor. Most temperature converters provide
the option to drive the output signal upscale or downscale when the sensor becomes
open-circuit to activate process protection or to warn the operators (open circuit
alarm).
Early Burnout Detection (EBD) enables the monitoring of the sensor connection to
detect increasing loop resistance which can forewarn of the sensor breakdown.
When the converter is powered up, or after re-connection of a thermocouple sensor,
the loop resistance is measured and stored as a reference. If the loop resistance
increases by more than 50ohms then the EBD alarm is activated (relay on and LED
lit). Note that this does not initiate upscale or downscale drive activity until the input
connection is detected to be an open circuit.
The alarm condition is reset and a new base value of loop resistance is stored after
the input thermocouple circuit is open-circuited (remove the connector) or the power
is interrupted.

10 .5 Pulse output

The Pulse Output on the pulse isolator can be switched off (high impedance) or
selected to provide any of the following options:
• 1:1
• toggle
• fixed pulse duration
The "1:1" option selection causes direct signal connection to the input. The output
signal frequency and phase conforms to the input (except shape deformation for high
frequency).
The "toggle" selection requires specification of a "divider" parameter, chosen in the
range 1 to 65534. The pulse output will then "change state" (high to low, or low to
high) every n input pulse.
th
The "fixed pulse duration" selection requires the specification of "divider" value and
pulse "duration" value. The pulse output will then create a fixed duration ON state
signal every n input pulse. The pulse duration can be configured anywhere in the
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range from 0.05 to 10ms, however care must be taken to ensure that the output
signal does not exceed a 50% duty cycle at the chosen maximum input frequency.
Refer to Section 7 .5 for screen views and further information.
The following figure shows input and output signal examples for all three available
options.
INM PCS45
Standard 4-20mA
characteristic
Full scale 0-20mA
characteristic
Input signal range
20.5mA
Signal limitation
according to NE43
Range
end
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