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The nanodac recorder/controller provides combined recording and
control in a single ¼ DIN package.
There are two control loops. One of these loops is used to control the
temperature. The second loop is used to control the enriching gas valve
and the dilution air valve.
A manual probe clean request and a sooting alarm relay is included.
The nanodac recorder/controller can accommodate a range of probes
from various manufacturers. A suitable probe is the Eurotherm ECprobe
which is interchangeable with all other carbon sensors. It is available in
600mm or 900mmm lengths with or without integral thermocouple in
types K, N, S, or R. A typical orde r code is CP600-K.
In addition to the features listed above, the nanodac recorder provides
powerful logging and secure archiving of data. It can store information in
either open CSV format or in a secure (UHH), check summed format to
protect data integrity.
In addition to live trending, a simple menu allows any selected portion of
the recorder history to be archived, either to a ‘memory stick’ plugged
into the USB port at the rear of the recorder (Local Archiving) or to a
computer or server, by means of the FTP protocol (Remote Archiving). The
archived data remains in the flash (50MB) memory of the instrument and
can be reviewed directly on the instrument display.
The archive period can be chosen between the last hour, last day, last
week, last month, archive everything in the recorders history or archive all
files created since or updated since the last archive.
The status of the archive is displayed on the nanodac recorder/controller
which shows when data is being transferred or is complete.
The archive data includes actual values from real or comms channels (PV),
Alarm Messages, and Operator Input Messages all of which are accurately
dated and time stamped from the on-board real time clock.
Purpose of this note
The purpose of this application
note is to describe how the
nanodac recorder/controller may
be used to control temperature
and carbon potential in metal heat
treatment furnaces. Using the
measurements of oxygen level and
temperature the nanodac
recorder/controller may be used to
calculate the carbon potential
levels using the Zirconia function
block.
Heat only Temperature Control and
Carbon Potential Control using the
nanodac Recorder/Controller
Application Note
nanodac™
Recorder/Controller
MODEL
Application Example
Channel 1 thermocouple input
Loop 1 is configured for heating control. The heating
channel is a time proportioning logic output used to drive a
solid state relay or thyristor unit.
The Zirconia block measures both oxygen and temperature
using input channels 2 and 3 respectively and a third virtual
channel is used to chart the level of oxygen.
Loop 2 is configured for carbon potential control using the
carbon potential output from the Zirconia block as the
process value.
Dilution air and enrichment gas is admitted to the furnace
using digital outputs 2 and 3 respectively.
Eurotherm Part No. HA030817U003 Issue 1 September 10 2 nanodac Application Note
Heat only Temperature Control & Carbon Potential Control
using the nanodac Recorder/Controller
Introduction
When mild steels or certain low carbon steels are heated at
temperatures above 900°C in a carbon rich atmosphere
the surface of the steel absorbs carbon by diffusion. The
depth of carbon enrichment depends on the time and
temperature of the treatment known as carburising. The
presence of carbon in the steel causes a change in its
physical properties.
A Zirconia probe is used to measure the level of oxygen. It
generates a millivolt signal based on the ratio of oxygen
concentration between the reference airside of the probe
(outside the furnace) and the amount of oxygen actually
inside the furnace.
The temperature of the furnace is measured using a
thermocouple. This may be a thermocouple mounted
within the Zirconia probe or installed as a separate item.
Together the temperature and oxygen level signals are
used by the nanodac recorder/controller to calculate the
actual percentage of carbon in the furnace atmosphere.
The carbon potential control loop increases the carbon
potential by opening a solenoid valve which allows a
carburising or enriching gas (e.g. propane) to enter the
furnace. Conversely, to decrease the carbon potential,
dilution air or nitrogen is introduced into the furnace.
The nanodac recorder/controller can trigger an alarm
when the atmospheric conditions within the furnace are
such that carbon will be deposited as soot on all surfaces
inside the furnace, including the workpiece. Avoiding
sooting protects the furnace lining, maintains the accuracy
of the zirconia probe and stops formation of a soot barrier
on the workpiece which can prevent carbon diffusion.
The nanodac recorder/controller has a probe cleaning
strategy that can be programmed to occur between
batches or manually requested by the operator. A short
blast of compressed air is used to remove any soot and
other particles that may have accumulated on the probe.
Once the cleaning has taken place the time taken for the
probe to recover is measured. If it is too long this indicates
that the probe is ageing and needs replacement or
refurbishment.
Furnace
Thermocouple
Screen
Thermocouple
Zirconia pellet
Outer
electrode
Inner
electrode
Heating
SSR
Dilution
Air
Enrichment
Gas
Power
Supply
Clean
Probe
3B
3A
N
L
2B
2A
1B
1A
LC
LA
2I
1–
1+
1I
2–
2+
4I
3–
3+
3I
4–
4+
I/O1
OP2
OP3
DIA
Soot
Alarm
C
4A
LC
LB
E
5A
Physical Wiring