Super System GOLD PROBE Installation Manual

Copyright 2005

GOLD PROBE

Release A

07/01/2005

INSTRUCTION MANUAL

M4501

SSiSUPER SYSTEMS INC.

7205 Edington Drive • Cincinnati, Ohio 45249 1-513-772-0060 • 1-800-666-4330 •

FAX [phone]

GOLD PROBE MANUAL

Table Of Contents

♦ Introduction .................. 1

♦ Specifications ............... 1

♦ Characteristics .............. 2

♦ Operating Theory .......... 3

♦ Installation .................... 4

♦ Maintenance .................. 5

♦ Troubleshooting ............ 7

♦ Control Systems ............ 8

♦ Warranty ..................... 10

GOLD PROBE MANUAL

INTRODUCTION

Thank you for selecting the Gold Probe™ for your atmosphere control application.

The Gold Probe™ represents “state of the art” in carbon sensor technology. It has been
designed for use in carbon control systems as applied to both carbon control in
atmosphere furnaces and dew point in endothermic generators.

The Gold Probe™, with its unique measuring electrode construction, is the product of a
team of design and application engineers, each with over twenty years of atmosphere
control experience. The SSi engineering team has long recognized that the sensor is the
most critical component in the atmosphere control system and has traditionally been the
weakest link. Now, reliability, repeatability and accuracy are assured with the inclusion
of the Gold Probe™ in your control system.

SPECIFICATIONS

♦ Useful %C Range- .01 to 1.6%
♦ Temperature Range- 1200°F to 2000°F

(649°C to 1093°C)

♦ Stability- within +/- 1 mVDC
♦ Impedance- less than 10 kohms @ 1700°F

(927°C)

♦ Useful output- 0 to 1250 mVDC

♦ Length- 21 1/2", 25 3/4", 35"

(546mm, 654mm, 889mm)

♦ Weight- 3.7, 4.0, 5.8 lbs
♦ Insertion- 14.3", 18.6”, 20”or 27.8"

(363mm, 472mm, 508mm,or
706mm)

♦ Mounting- 1" (25.4mm) NPT
♦ Sheath dia.- 0.84" (1/2" pipe)

(21mm, 13mm pipe)

1

GOLD PROBE MANUAL

CHARACTERISTICS

The typical zirconia carbon sensor consists of a
closed end tube with the sensing portion at the tip.
The entire tube may be zirconia or there may be a
slug of zirconia cemented in the tip. Fig.1
illustrates the Gold Probe™ design with details
omitted for clarity. The tip of the tube is spring
loaded into contact with the sheath, which also
serves as the outer electrode. The inner electrode
is spring loaded into contact with the inner
zirconia surface. A thermocouple is positioned
close to the inner electrode surface and reference
air bathes the sensing surface.

FIG. 1

To the instrument technician, the probe looks like
a battery (see Fig.2.) It displays a voltage, Ec, from

which the carbon potential can be calculated. The
probe thermocouple is shown next to the sensing
electrode.

The value of the internal resistance can be
measured, as shown in Fig. 3, by putting a shunt
resistor across the probe, measuring the resultant
voltage, Em and carrying out the simple calculation

shown.

FIG. 2

FIG. 3

2

BASIC OPERATING THEORY

Carbon potential of a conventional furnace

atmosphere is defined as the %C achieved in a
coupon of carbon steel shim stock equilibrated in
the furnace atmosphere. Unfortunately,
equilibration time is long, so it is impossible to
continuously control the atmosphere on the basis
of shim stock measurements. A zirconia sensor,
however, can be used to measure and control the
carbon potential precisely, and on a continuous
basis.

Strictly speaking, the zirconia probe is not
sensing carbon at all. It is an oxygen sensor with
a mVDC output described by Equation (1).

Fortunately, an empirical (experimental)
relationship exists between oxygen concentration
and carbon potential, and this relationship has
been used in carbon control instruments since the
early ‘70’s. The equation used by most control
manufacturers today is illustrated by Equation
(2), which states that there are only three
variables affecting the measured millivoltage.
Because the actual equation used is somewhat
complex, it is not reproduced here. A full
description of probe theory will be found in SSi
technical bulletin T4401 (Zirconia Sensor
Theory).

GOLD PROBE MANUAL

ZIRCONIA O2 RESPONSE

Ec = 0.0276TR log (Pf /Pa) millivolts (1)

Zr PROBE ALGORITHM

%C= ( EC , %CO, TR) mVDC (2)

Where: means ‘is a function of’
%C is the carbon potential
%CO is carbon monoxide percentage

TR is the absolute temperature in degrees
Rankine (deg. F + 460).

All competitive probes will invariably agree
within one or two millivolts when exposed to the
same atmosphere under equilibrium conditions.
Differences in values listed by probe vendors
relate to differences in manufacturers’ source
data, but the true value of the zirconia probe is its
repeatability.

and E

is the probe output in millivolts.

C

3

GOLD PROBE MANUAL

INSTALLATION

If your new probe is to be installed in an existing
probe entry, be advised that your warranty
requires that the probe should extend no more
than 4" (101mm) into the furnace chamber. This
is because, at operating temperatures, the sheath
can sag enough to cause breakage of the zirconia­sensing element.

For new installations, an entry fitting must be
provided at the furnace wall to permit the probe
to extend from 2" to 4" (51mm to 101mm) into
the furnace chamber. Listed here are several
conditions that should be considered when
choosing a location for the entry fitting. Most of
these conditions allow for some compromise, and
represent, at best, recommendations.

A variety of fittings have been used to provide
the 1" (25.4mm) NPT entry. The simplest is the 1
1/2" (38mm) coupling, as shown in Fig. 4.

NOTE:

Your Gold Probe™ has been thoroughly
tested in our controlled atmosphere furnace.
Therefore, the sheath shows evidence of
thermal discoloration.

ENTRY FITTING LOCATION

♦ In top third of work zone......

♦ Close to control thermocouple......

♦ Distant from radiant tubes......

♦ Away from carrier gas entry......

♦ Clear of work baskets......

The furnace is prepared by drilling a 1 1/2"
(38mm) diameter hole through the wall and the
insulation. The hole must be at right angles to the
wall to avoid interference with probe insertion.
The fitting is then welded or screwed to the wall
to provide a gas-tight entry.

Your Gold Probe™ has been shipped with an o-
ring compression fitting which allows you to
adjust the insertion. Manual tightening of the cap
is adequate for side mounting. A wrench should
be used for vertical mounting to assure probe will
not move. When installing in a hot furnace, insert
the first four inches directly, then at a rate of 2"
(51mm) per minute in order to avoid thermal
shock fracture.

4

WARNING
Zirconia is thermal shock sensitive. Insert
into hot furnace no faster than 2" (51mm)

per minute (after first 4 inches or 101

millimeters).