Omega Products MCJ Installation Manual

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MCJ SERIES

Miniature Cold

Junction Compensator

omega.com

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is constantly pursuing certification of its products to the European New Approach Directives. OMEGA will add the CE mark
to every appropriate device upon certification.
The information contained in this document is believed to be correct, but OMEGA accepts no liability for any errors it
contains, and reserves the right to alter specifications without notice.
WARNING: These products are not designed for use in, and should not be used for, human applications.

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Unpacking Instructions

Remove the Packing List and verify that you have
received all equipment, including the following
(quantities in parentheses):

MCJ Cold Junction Compensator (1)
Mating male OST thermocouple connector (1)
Thermocouple male pins (2)
Battery (1)
Operator’s manual (1)

If you have any questions about the shipment, please call
the Customer Service Department at 1-800-622-2378 or

203-359-1660. We can also be reached on the Internet at
www.omega.com
e-mail: [e-mail]

When you receive the shipment, inspect the container
and equipment for signs of damage. Note any evidence
of rough handling in transit. Immediately report any
damage to the shipping agent.

NOTE

The carrier will not honor damage claims unless all
shipping material is saved for inspection. After examining
and removing contents, save packing material and carton
in the event reshipment is necessary.

i

ii

MCJ Series Miniature

Cold Junction Compensator

TABLE OF

CONTENTS

Section Page

Section 1 Introduction . . . . . . . . . . . . . . . . . . . .1-1

1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . .1-1

1.2 Theory of Operation . . . . . . . . . . . . . . . . . . .1-3

Section 2 Operating Instructions . . . . . . . . . . .2-1

2.1 Battery Installation . . . . . . . . . . . . . . . . . . . . .2-1

2.2 To Test the Battery . . . . . . . . . . . . . . . . . . . .2-2

2.3 To Measure Temperature . . . . . . . . . . . . . . .2-2

2.4 To Calibrate Thermocouple Instruments . . . .2-6

Section 3 Troubleshooting and Calibration . .3-1

3.1 Troubleshooting the MCJ . . . . . . . . . . . . . . .3-1

3.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

Section 4 Specifications . . . . . . . . . . . . . . . . . .4-1

Section 5 Retrofit Kit . . . . . . . . . . . . . . . . . . . . .5-1

1-1

Introduction

1

1.1 Description

The MCJ Miniature Cold Junction Electronic Ice Point is
an automatic cold junction compensator that is
necessary to utilize when using a thermocouple (T/C)
probe together with a voltmeter (or millivolt recorder) to
measure temperature. It is also necessary to utilize when
a precision millivolt source is used to calibrate a
thermocouple meter. The MCJ should be used with
instrumentation that has an impedance of 50K ohms or
greater.

Figure 1-1. MCJ

1-2

Introduction

1

This extremely versatile, battery-powered device
provides the electrical equivalent of an ice bath
reference at 32° F (0°C ). It is factory calibrated and
available in one of nine thermocouple calibrations:

T/C

TYPE METALS

J Iron/Constantan
K Chromega

®

/Alomega

®

T Copper/Constantan
E Chromega®/Constantan
R Pt-13% Rh/Pt*
S Pt-10% Rh/Pt*
G W/W-26% Re*
C W-5% Re/W-26% Re*
D W-3% Re/W-25% Re*

*Where: Pt = Platinum, Rh = Rhodium,

W = Tungsten, Re = Rhenium

MCJ’s manufactured before 1996 use a different battery
and battery compartment. See Section 5 about kit for
retrofitting pre-1996 units.

Introduction

1

1-3

1.2 Theory of Operation

The MCJ contains a self-compensating voltage
generator that is built into a small housing. The input side
consists of the standard “OST” female pins that are
integral to the MCJ case (see Figure 1-2). On the output
side are two screw terminals that are connected to the
compensating voltage circuitry.

Figure 1-2. Inside the MCJ

1-4

Introduction

1

This design incorporates a temperature sensitive element
that is thermally integrated with the “cold end” junctions
T2 and T3 (located inside the MCJ). In theory, as the
ambient temperature surrounding T2 and T3 varies, a
change in thermal emf is generated.

The thermal emf induced by this change in ambient
temperature will create an error in the output signal,
unless it is compensated for. To correct the error, an
equal and opposite voltage is automatically injected into
the circuit by the compensating voltage generator circuitry
of the MCJ. This, in turn, cancels out the emf error.

By integrating copper leads at the cold end junctions T2 and
T3, the thermocouple material itself is not directly connected
to the voltmeter, thereby eliminating induced errors. This
also eliminates the need to run thermocouple lead wires
from the output of the MCJ to the measuring device.

The compensating voltage generator in the MCJ is
temperature sensitive and produces a compensating emf
that tracks the error signal over a wide ambient
temperature range with a high degree of accuracy.