WIKA TWG User Manual

INSTRUCTION MANUAL

NI-401E

Rev. 3 07/99

TEMPERATURE SWITCHES

WEATHERPROOF: SERIES TWG EXPLOSIONPROOF: SERIES TAG

One contact

Stem type “B” Stem type “C” Stem type “ F”

A = bulb connection
B = cable entry

PESO 2,1 kg dimensions in mm PESO 2,9 kg dimensions in mm

NOTE: dimensions and weights are not binding unless released on certified drawings.
CAUTION

• Before installing, using or carrying out maintenance on the instrument it is necessary to read and understand the
indications given in the attached Instruction Manual.

• The instrument must only be installed and maintained by qualified personnel.

• Installation must only be carried out following verification of the congruity of the instrument features with the plant

and process requirements.

• The functional features of the instrument and its degree of protection are shown on the identification plate fixed to the
case.

CONTENTS:

1 - GENERAL NOTES
2 - OPERATING PRINCIPLE
3 - SET POINT REGULATION
4 - SET POINT CALIBRATION
5 - MOUNTING AND CONNECTIONS
6 - INSTRUMENT PLUMBING

X = Bulb sensitive portion
Y = Insertion length
K = Capillary length

A = bulb connection
B = cable entry

7 - PUTTING INTO OPERATION
8 - FUNCTIONAL VERIFICATION
9 - TROUBLESHOOTING
10 - STOPPING AND DISMOUNTING
11 - DEMOLITION

Two contacts

X = Bulb sensitive portion
Y = Insertion length
K = Capillary length

All data, statements and recommendations supplied with this manual are based on information believed by us to be

reliable. As the conditions of effective use are beyond our control, our products are sold under the condition that the
user himself evaluates such conditions before following our recommendations for the purpose or use foreseen by him.

The present document is the property of ETTORE CELLA SPA and may not be reproduced in any form, nor used for
any purpose other than that for which it is supplied.

INSTRUCTION MANUAL

1 - GENERAL NOTES

1.1 FOREWORD

The wrong choice of a series or a model, as well as the
incorrect installation, lead to malfunction and reduce
instrument life. Failure to follow the indications given in this
manual can cause damage to the instrument, the
environment and persons.

1.2 ALLOWED OVERRANGE

Temperatures exceeding the working range can be
occasionally tolerated provided they remain within the
limits stated in the instrument features (vacuum or proof
temperature). Continuous temperatures exceeding the
working range can be applied to the instrument, provided
they are clearly stated in the instrument features. The
current and voltage values stated in the technical
specifications and ratings must not be exceeded.
Transitory overranges can have a destructive effect on the
switch.

1.3 MECHANICAL VIBRATIONS

Can generally lead to the wearing of some parts of the
instrument or cause false actuation. It is therefore
recommended that the instrument be installed in a place
where there are no vibrations. In cases where this is
impossible it is advisable to take measures to lessen the
effects (elastic supports, installation with the pin of the
microswitch positioned at right angles to the vibration
plane, etc.).

1.4 TEMPERATURE

Due to the temperature of both the environment and the
process fluid, the temperature of the instrument could
exceed the allowed limits (normally from -20° to +70°C).
Therefore, in case it does, suitable measures (protection
against heat radiation, heated cabinets) must be taken.

2 - OPERATING PRINCIPLE

fig. 1 - Electrical connections and adjustment screws

One contact instruments Two contact instruments

The thermometric bulb is constituted by a rigid constant­volume container. It is connected via capillary tubing to a
pressure measuring element (bourdon tube). This system
is filled with gas, and its absolute pressure is proportional
to absolute temperature (Charles’ law). As a consequence,
any change in bulb temperature causes a change in gas
pressure acting on sensible element, causing its free tip to
undergo an elastic deflection which is used to actuate one
or two electrical microswitches adjusted at prefixed set
point values.

3 - SET POINT REGULATION

3.1 Each microswitch is independent and can be

regulated by means of a screw (for adjustment) in such a
way that it actuates when the temperature reaches
(increasing or decreasing) the desired value (set point).

3.2 The instrument is usually supplied with the switches
set at 0°C or at the lowest setting range value if this is
higher than 0°C (factory calibration).

3.3 The instrument is supplied with an adhesive label
showing the set point calibration value. With factory
calibration the values are not indicated on the label, as
these are temporary and will be modified with the definitive
values.

3.4 Prior to installation the instrument must be calibrated
and the definitive calibration values written on the
adhesive label using a suitable indelible ink pen.

3.5 If the instrument has been expressly ordered with
specific calibration, it is a good rule to check the

calibration values stated on the adhesive label, prior to
installation.

3.6 The position of the adjustment screws is given in fig. 1.

3.7 The effect that the direction of rotation of the

adjustment screws is described on the adhesive label.

NI-401E

Rev. 3 07/99

1 - Microswitch set point calibration screw
3 - Terminal block
4 - Electrical connection identification plate

Designation of the contacts:
C - Common
NA - Normally Open
NC - Normally Closed

1 – Microswitch 2 set point calibration screw
2 – Microswitch 1 set point calibration screw
3 – Terminal block
4 – Electrical connection identification plate

Microswitch electrical circuit: State of the contacts at initial temperature
range (when factory calibrated)