VICI ITC User Manual

Valco Instruments Co. Inc.

Instrumentation
Temperature Controller
Instruction Manual

P. O. Box 55603, Houston, TX 77255

[phone]

•

Sales toll-free [phone]

Fax [phone]

MAN-ITC

Rev. 8/96

Printed in USA

Table of Co ntents

1. GENERAL DE SCRIP TION. ...... .... .... ...... .... .... .... ...... .... .... ...... .... .... ...... .... .... ...1

1.1 Standard Features

1.11 Thermocouple Sensor

1.12 Proportional Heater Power Control

1.13 Power Attenuation

1.14 Zero Crossover Power Application

1.15 Digital Temperature Setting

1.16 Compact Rugged Construction and Functional Layout

1.2 Specific ations and Model Codes

1.3 Technical Description

1.31 Thermal System Overview

1.32 ITC Block Diagram by Function

1.321 Input Amplifier

1.322 Thumbwheel Switches and D/A Converter

1.323 Differential Comparator

1.324 Heater Power Switch

1.325 Thermocouple Break Detection

1.326 Proportional Power Control

1.327 Power Attenuation

1.33 Proportional Power Control

1.34 Power Attenuation

Pag e

2. OPERATION . .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .10

2.1 PHYSICAL LAYOUT OF THE ITC

2.2 Thermocouples

2.3 Setpoint (Set °C)

2.4 Propor tioning Bandwidth

2.41 Bandwidth Defined

2.5 Install ation

2.6 Troubleshooting and Schematic Di agram

2.61 Situation:
PWR ON indicator fails to illuminate; instrument does nothing.

2.62 Situation:
TCPL indicator ON continuously; no power applied to heater

2.63 Situation: No power being applied to heat er ; TCPL indicator OFF.

3. WARRANTY ............... .......... ........ ........ .......... ........ ........ .......... ........ ........ .....19

4. TECHNICAL DRAWINGS .................... .............. ................ .............. .............20

1. INTRODUCTION AND GENERAL DESCR IPTION

The Instrumentation Temperature Controller (ITC) is an isothermal temperature
controller intended for broad spectrum usage in thermal systems common to
modern analytical instrumentation. The instrument is designed to be a flexible
building block with which the user can config ure a ther mal system to suit p art icular
requi rements. Althoug h the contr oller is only a si ngle elemen t in such a sys tem,
its flexibility and performance ultimately determine the stability, reproducibility, and
accuracy of the enti re syst em.

Inasmu ch as we do no t attempt to prese nt a por tfolio o f specif ic appli cations, t his
manual is m ore gener al th an sp ecif ic. Inst ead, we ar e att empti ng t o str ike a spar k
of in tuitive understa nding a nd intere st for how the ITC functio ns. Th e ITC’s func­tion an d relat ionsh ip to therm al syst ems ar e the mos t valuable n otion s transm itte d
by this manual. Just as there i s no appl icati on manua l for vice- grip pliers, there i s
not an application manual for the ITC. Both are basic, extremely useful devices,
whose rea l worth is det ermined by th e use r.

1.1 Standard Feat ures

1.11 Thermo couple Sen sors

The ITC utilizes thermocouple sensors fabricated from ordinary thermocouple wire.
A variety of factor s lea d to th is b eing th e bes t choi ce of senso rs:

•

Sensor junctions of very low mass can be easily fabricated. Lower mass
means quicker recognition of temperature changes.

•

Thermocouples are inherently rugged, requiring little in the way of special
handling precautions.

•

Thermocouple wire is inexpensive and readily available.

In keeping with this choice of sensors, the instrument is appropriately equipped
with:

•

Automatic reference junction compensation.

references to 0°C, regardless of ambient temperature.

•

Thermocouple break detection.

power circuitry will be disabled, and a front panel indicator illuminat ed.

•

High impedance differential input circuitry.

instrument to tolerate floating or grounded thermocouples, with high
common-mode noise immunity.

The ea se o f fabr ic atio n for sens ors compa tible wit h th e IT C is suc h th at us ers can
seriously consider making their own. (In many cases, all that is needed is a small
torch, silver solder, and a roll of thermocouple wire.)

Should the ther mocouple break, the heater

Circuitry automatically

This circuitry allows the

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1.12 Proportional Heater Power Control

The ITC utiliz es propor ti onal power applic ation t o minimiz e temper ature overs hoot,
and improve temperature stability about the setpoint. Controls are accessible to
the user, allowing the proportioning bandwidth (in

o

C) to be adjusted to meet

specific requirements.

1.13 Power Attenuation

Many te mperatu re co ntroll ers a re used in con junct ion wit h vari acs (var iable o utput
transformers) in order to improve temperature stability. By reducing the maximum
power available to the heater, the user is adjusting the heater "size" to suit his
particular thermal system. This is a practical, flexible solution to the problem, but
requi res two devi ces to con trol the t emperatu re, one of whi ch is heavy, ineffi cient,
and expensive.

The ITC employs a pushbutton switch so the user can attenuate the total power
available to the heater circuit. Attenuation is selectable from 0 to 90%, in incre­ments of 1 0% .

1.14 Zero Crossing Power Application

Power is applied to the load in increments of integral half cycles, only. This
technique drastically reduces RFI/EMI normally associated with high current AC
switching.

1.15 Digital Temp erature Setting

The ITC employs a bank of three digital thumbwheel switches for temperature
setpoint selection. The setpoint is selecta ble in 1

o

increments. The most obvious

advanta ge t o thi s s che m e is 10 0% se tt i ng r epe at abi l ity.

1.16 Compact Rugged Cons tructio n and Func tional Layout

The ITC’s physical characteristics are strictly utilitarian. In all cases, rugged
construction techniques are employed, insuring that the assembled instrument is
not delivered by a freight company in kit form. The instrument is housed in an
aluminum/cycolac enclosure measuring 2.4" x 8.3" x 5.9". The top of the enclo­sure c an b e qu ickl y r em oved, a l low ing ac ces s to al l f u ses, e lec tr on ic s, etc.

It is worthy of note that almost all electronic components are mounted on a single
printed circuit board. This feature directly translates to simple troubleshooting
methods and minimal spare parts inventory.

2

1.2 Product Numb ers and Spe cifications

Produc t Nu mbe rs: ITC 10 X

X corresponding to
399 for 0°C to 399°C range
999 for 0°C to 999°C range

Example:
ITC103 99: ITC, 1000 watts m aximum he ate r power, 0°C to 399°C range

Sensor Requirem ent Thermocouple; Ty pe K
Range 0° to 390°C, or 0° to 999°C, as ordered

Absolute Accurac y

±

.5% of full scale
Repeatability .5°C at constant ambient
Sensit i ti vi ty to Am bi en t Ch an ge s . 05° C per ° C c ha nge
Operati n g A mbi en t 10° t o 5 0°C
Switched AC Power 1000 watts;

zero-crossing erro r: 5V AC max.

Proportioni ng Ba ndwi dt h

±

3

°C

Proportioni ng Freque nc y 2 Hz
Setpoint 1° C increments; push button selection
Max. Power Input Requirement 10.0 amps at 117 VAC
Power Attenu ati o n 0 to 90 % in 10% i ncr eme nt s
Physical Dimensions 2.4" x 8.3" x 5.9"; weight 1 lb. 14.4 oz.
Visual I ndi c at or s

•

Power On (PWR) - illuminated whenever the instrument is plugged
into a source of 120V AC, and the PWR switch is in the ON position

•

Heater On (HTR) - illuminated whenever the controller applies
power to the heater

•

Thermocouple Fault (TCPL) - illuminates whenever thermocouple sensor
opens. (If a sensor failure is detected, heater power is automatically
interrupted, and t he HTR i ndicator will remain O FF.)

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1.3 Techn ical Description

A general knowledge of the ITC’s organization and operation is helpful to its
successful implementation. To facilitate understanding, three questions are posed:

1. What position does the ITC occupy in a thermal system?

2. How is the ITC organized to accomplish its task?

3. What is the most important aspect of the ITC’s organization?

These ques t io ns ar e a nswere d by Se ct ion s 1 . 31, 1.3 2, and 1 . 33, re sp ect ive ly.

1.31 Thermal System Overview

Figure 1

depicts a generalized closed-loop control system. The system is termed
closed-loop since the controller bases its corrective actions on the actual status of
the controlled function. In an open-loop system, corrective actions are based on
anticipated stat us. Closed-loop syste ms are defi nitel y pre ferable.

CONTROLLED

FUNCTION

SENSOR

CONTROLLER

CORRECTION

ELEMENT

Figure 1

The system is compr ised of:

•

Controlled Fu nction .

•

Sensor.

•

Controller.

Appropriate to the function; level sensor, pressure transducer, etc.

Determines when corrective action is necessary, based on

Water level, air pressure, etc.

information supplied by the sens or.

•

Correction Element.

Means of adding water, increasing pressure, etc.

With slight modification, the diagram becomes appropriate to a thermal system
utili zing an ITC, as show n in

Figure 2

.

HEATED

ZONE

THERMOCOUPLE

INSTRUMENTATION

TEMPERATURE

CONTROLLER

(ITC)

HEATER

Figure 2

4

It is readily seen that the ITC is responsible for maintaining the temperature within
the heated zone. However, proper selection and application of the thermocouple
and heater are essential if the ITC is to perform its function. (Refer to Section

2.2.)

1.32 ITC Block Diagram by Function

Almost any electronic device can be described by a block diagram of its circuit
elements, each element performing something essential to the function of the
device. Indeed, such a diagram is typically the first state in its design. Further,
devices of simi lar fu nction wil l have simila r block diagrams.

TCPL

BREAK DE-

TECTION

SENSOR

SET POIN T

SELECT

INPUT

AMP

D/A

CONVERTER

DIFFER E NT I AL

COMPARATOR

ZERO

CROSSING

SWITCH

POWER

ATTE NUATOR

HEATER
POWER
SWITCH

Are these blocks supposed
to correlate to items in

PROPORTIONAL

POWER

CONTROL

1.321 and following? No­menclature needs to be
consistent. RC

Figure 3

The function of the ITC is to control the temperature in a heated zone. A brief
discussion of what is required to perform the function reveals the elements
conta ine d i n i ts bl ock dia gra m,

Figure 3

.

1.321 Input Amplifier

The signal supplied by the thermocouple is too small to be recognized by the other
circ uit el ement s (appr ox. 50 microvolts /

o

C). Therefore, t he si gn al m ust b e amp l ifi e d

to a us ef ul level .

1.322 Set Point Selectors and D/A Convert er

The th umbwheel sw itches provi de a means of repre senting th e desired t empera­ture within the heated zone. (This temperature is hereafter referred to as the

setpoint

.) The switches prov ide a digit al repres entation o f the setpoi nt, which i s
then c onverted to a more useful s ignal by mea ns of a te n-bit D/A convert er. The
D/A converter conforms to the same transfer function as the input amplifier; i.e., a
representation of 100° C by the input amplifier is identical to the D/A converter’s
repres ent a ti on of 10 0

o

C.

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1.323 Differential Comparator

A dif ferential comparat or is u sed to co mpare the output o f the D/ A converte r with
that of the inp ut ampl ifier. Subsequent ly, the com parator ’s output den otes whe ther
the zo ne t emp era t ur e is hi gh er or l ower tha n the se t poin t .

1.324 Heater Power Switch

In accordance with the comparator’s decision, the power circuitry will apply power
to the hea ter wh en t he zone temper atur e is below t he s etpoi nt a nd int err upt power
when i t i s ab ove th e s etp oi nt .

In strictly theoretical terms, the above four elements are all that would be required
to imp leme nt th e contr olle r’s fun ction . However, prac tical appl ica tion r equi res three
additional elements:

1.325 Thermocouple Break Detection

The most common physical malfunction in thermocouples is a break, or open
circuit. If a break occurs, the input amplifier can no longer report the zone
temperature, and usually will report the ITC’s temperature, instead. From the
preced ing d isc ussi on, one can de duce t hat t his i s a pot enti all y disa stro us s ituat ion.
However, a separate circuit is employed specifically to detect a break condition. Its
output will cause the Heater Power Switch to be disabled, and a front panel
indicator to be illuminated whenever a break occurs.

1.326 Propor tional Power Control

To this point, power application to the heater has been described as simply
"appl ied or inte rrupted ". In rea lity, this would be anal ogous to tr ying to m aintain a
dragster’s speed at 30 mph using full throttle applications only. Obviously, power
must be delivered according to the need. For this reason, the ITC employ s pro­portional power control, where net power is delivered to the heater according to
the difference between the setpoint and zone temperature. The proportioning
technique is discu ssed in Se ction 1.33 .

1.327 Power Attenuation

Effective heater size can be tailored to the application by proper adjustment of the
power a ttenu atio n con tro l. Exce ssive h eat er rat ings ar e oft en t he ca use o f sys tem
instability at near ambient temperatures. Proportional control and power
attenuation work hand-in-hand to produce excellent temperature stability. (Refer to
Section 2.3.)

1.328 Zero Crossing Switch

This allows the he ater to come on only if t he AC wavefor m is at zero to supp ress
noise on th e p ower li ne.

1.33 Propor tional Power Control

Alth ough t he IT C’s inpu t amp lifi er a nd D/A ci rcui tr y are acc urate and predi cta ble in
their temperature representations, they do not in themselves constitute a good
temperature controller. In a control system, the essential factor is stability. A
temperature controller is not doing its job if the zone temperature is allowed to
oscil late about the setpoint to a degree which upsets the process. In shor t, the
aim is to reduce a thermal system’s natural tendency to oscillate to a level where it
is not significant.

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