Stanford Research Systems SR630 Data Sheet

· 16 channels

· B, E, J, K, R, S and T type thermocouples

· 0.1 °C resolution

· Displays °C, °F, K and VDC

· 2,000 point non-volatile memory

· Four analog outputs proportional to
to temperature

· GPIB, RS-232 and printer interfaces

· SR630 ... $1495

(U.S. list)

Stanford Research Systems phone: [phone]

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Temperature Monitor

The SR630 is a 16-channel thermocouple monitor designed to
read, scan, print and log temperatures or voltages. You can use
any one of seven standard thermocouple types to read
temperatures from −200 °C to +1700 °C. For remote
monitoring applications, the SR630 can time-stamp and store
up to 2000 readings in non-volatile memory for later analysis.

Temperature readings from the SR630 can be viewed on the
front panel or queried via the instrument's standard RS-232 or
GPIB interfaces. In addition, the standard Centronics printer
port provides convenient hardcopy output in either tabular or
strip chart format.

Voltage Monitor

The SR630 can also be configured as a 16-channel DC
voltmeter with full-scale ranges from 30 mV to 100 V (1 mV
resolution). As a voltmeter, the unit has 0.05 % accuracy and
1 µV input offset drift. Each channel can be set independently
to monitor either temperature or voltage, giving the SR630
even more flexibility in your application. Four rear-panel
outputs are also available to provide a voltage proportional
to the temperature of the first four input channels. The
voltage outputs can be used to drive recorders or to control
external instrumentation.

SR630 Thermocouple Monitor

Thermocouple Monitor

SR630  Thermocouple monitor (16-channel)

www.thinkSRS.com

Inputs

Sixteen screw-terminal inputs are mounted on a rear-panel
isothermal block for cold junction compensation. The isolated
differential inputs have a 250 V breakdown level, allowing the
SR630 to tackle difficult applications such as temperature
profiling of electrically live equipment. Each of the 16 channels
may be independently set to display in units of °C, °F, K, mV
or V. Similarly, thermocouple type, nominal temperature,
temperature limit, and alarms may be uniquely set for each
channel, providing complete flexibility in the configuration of
the instrument. Access to any channel parameter is provided
through the front panel or via the computer interfaces. The
SR630 can store up to nine instrument configurations including
thermocouple type and temperature limits for all 16 channels.

Outputs

There are four analog outputs that are proportional to the
readings on channels one through four. Both the slope (m) and
offset (b) of the equation, Vout = ±mX + b, are changed by
setting the nominal temperature and chart span for the
corresponding channel. X is either temperature or voltage,
depending on the setting for each channel.

You may use the analog outputs to drive chart recorders, or
they can provide a feedback signal for proportional
temperature control systems. They may also be used as fixed­level, analog control signals (set via the computer interfaces).

Alarms

Each channel can be programmed individually with an upper
and lower temperature limit. An audio alarm and a relay
closure indicate when any channel exceeds its preset
temperature or voltage limits. The front-panel LED display
will indicate which channel has exceeded its limit.

Data Logging

An internal, battery backed-up clock/calendar is used to time­stamp temperature readings. The SR630 can be set to scan,

time-stamp, and record data on up to 16 channels at
intervals from 10 to 9999 seconds. Data is either sent
immediately to the printer or stored in the internal 2,000 point
buffer for output at a later time (via GPIB or RS-232).

Built-In Printer Interface

A standard Centronics printer interface makes it simple to get
hardcopy output of temperature or voltage scans. Two
hardcopy formats are provided. The SR630 can print a
continuous strip chart showing up to 16 different temperatures
(see the example below). In addition, data can be printed in a
tabular format (see the example below and left) which logs the
time, date, and temperature or voltage for each channel.

Analog Multiplexer

The SR630 can also function as a 1:15 analog multiplexer.
Any of the first 15 input channels can be switched out to
channel 16 and passed on to other instruments. This feature is
useful in ATE systems and many other monitoring applications.

Available Thermocouples

Although the SR630 will read types B, E, J, K, R, S and T
type thermocouples, for many applications type K
(Chromel/Alumel) will serve well. K-type thermocouples
offer a wide temperature range (-200 °C to +1250 °C), low
standard error, and good corrosion resistance.

SR630 Thermocouple Monitor

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Tabular output

Strip chart output

Thermocouple

Channels 16
Thermocouple types B, E, J, K, R, S, T
Display units °C, °F and K
Display resolution 0.1 °C
Temperature displays Actual, Nominal, or Offset
Accuracy 0.5 °C for J, K, E and T

1.0 °C for R, S and B
Errors are for the SR630 only.
Standard errors for thermocouple
wire are 2 to 5 times the error due
to the SR630.

Inputs

Channels 16
Input type Independent, floating and differential
Input resistance 10 MΩ between + and − terminals,

>1 GΩ to ground

Input capacitance 0.001 µF
Input bias current <100 pA
Input protection 250 Vrms
Open circuit check 250 µA
Common mode ±200 VDC

Voltmeter

Full-scale display (±9.999, ±99.99 or ±999.9) mVDC,

(±9.999 or ±99.99) VDC
Range select Automatic
Resolution ±1 of least significant displayed digit
Offset ±2 of least significant displayed digit
Gain accuracy 0.05 %
Conversion rate 10/s for 50 Hz line, 12/s for 60 Hz
Line rejection >100:1

Scanning and Data Logging

Scanning Selected channels will be scanned.

Dwell time between scans is set

from 10 s to 9999 s.
Alarm Temperature or voltage limit for

each channel
Scan enable All channels may be scanned

or skipped
Printer output Voltages, temperatures, time and

date as a list or in a graphical format
Data memory Last 2000 measurements in battery

backed-up memory

SR630 Specifications

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General

Analog outputs Four analog voltage outputs

proportional to temperature of

channels 1, 2, 3 and 4
Relay output Switching 10 A
Store and recall Nine locations for instrument set-up
Interfaces RS-232, GPIB and Centronics

ports (standard). All instrument

functions may be set and read via

RS-232 or GPIB.
Power 10 W, 100/120/220/240 VAC,

50/60 Hz
Dimensions 8.5" × 3.5" × 13" ( WHD )
Weight 9 lbs.
Warranty One year parts and labor on defects

in materials and workmanship

Ordering Information

SR630 Thermocouple monitor $1495
O630KF1 K-type thermocouples, $50

5', fiberglass, qty. 5

O630KF2 K-type thermocouples, $75

10', fiberglass, qty. 5

O630KT1 K-type thermocouples, $50

5', teflon, qty. 5

O630KT2 K-type thermocouples, $75

10', teflon, qty. 5

O630RMD Double rack mount kit $85
O630RMS Single rack mount kit $85

SR630 rear panel

It has been known for a long time (Seebeck, 1822) that a
voltage exists across the junction of dissimilar metals. Figure 1
shows a thermocouple junction formed by joining two
metallic alloys, A and B. The voltage across the thermocouple
junction depends on the type of metals used and the
temperature of the junction. The mechanism responsible for
this voltage is quite complicated; however, there are certain
phenomenological results which make the effect useful for
measuring temperature.

Fig. 1 Thermocouple junction

The first of these results is that the voltage is approximately
linear with temperature. The change in junction voltage as a
function of junction temperature is given by the equation:

∆V= a ×∆T

where "a" is the Seebeck coefficient. The magnitude of this
coefficient depends on the metals used to form the junction;
typical values range from 0 to 100 µV/°C.

Nonlinearities

Unfortunately, the magnitude of the coefficient depends on
temperature. It is generally smaller at low temperatures, and
may change by more than a factor of two over the useful
operating range of a thermocouple. Despite this non-linearity,
the induced voltage is (usually) a monotonically increasing
function of temperature, and the voltages generated by certain
pairs of dissimilar metals have been accurately tabulated.
These tabulated values are referenced to the voltage seen
across a junction at 0 °C.

Additional Junctions

A problem arises when measuring the voltage across a
dissimilar metal junctiontwo additional thermocouple
junctions form where the wires connect to the voltmeter (Fig. 2).
If the wire leads which connect to the voltmeter are made of
alloy "C", then there exist thermal EMFs at the A−C and

SR630 Thermocouple Monitor

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B−C junctions. There are two approaches to solve this
problem: use a reference junction at a known temperature, or
make corrections for the thermocouples formed by the
connection to the voltmeter.

Fig. 2 Additional junctions

Figure 3 shows the use of a "reference" or "compensating"
junction. With this arrangement, there are still two additional
thermocouple junctions formed where the compensated
thermocouple is connected to the voltmeter. However, the
junctions are identical (they are both junctions between alloys
A and C). If the junctions are at the same temperature, then the
voltages across each junction will be equal and opposite, and
will not affect the measurement. Typically, the reference
junction is held at 0 °C (by an ice bath, for example) so that
the voltmeter readings may be used to look up the temperature.

Fig. 3 Reference junction compensation

The Thermocouple Effect

Junction @

T emperature T

A

B

Junction @

T emperature T

A

C

V

B

Unintended Junctions

C

A

Junction AB

B

Junction AB

C

V

C

A

Ice Bath

Compensation Without Reference Junctions

The second approach to the problem relies on the fact that the
voltage across the junction A−C plus the voltage across the
junction C−B is the same as the voltage across a junction of
A−B. As long as all the junctions are at the same temperature,
the presence of an intermediate metal (C) has no effect. This
allows us to correct for the voltage seen by the voltmeter in
Figure 2 by measuring the temperature at the A−C and B−C
junctions, and subtracting the voltage which we would expect
for an A−B junction (at the measured temperature). In the
SR630, the temperature of the A−C and C−B junctions is
measured with a low-cost, high-resolution semiconductor
detector, and the subtracted voltage is the tabulated voltage of
the A−B thermocouple at the measured temperature of the
A−C and C−B junctions. The advantage of this method is that
any type thermocouple may be used without having to change
compensation junctions or maintain ice baths.

Characteristics of Thermocouple Types

Any two dissimilar metals may be used to make a
thermocouple. Of the infinite number of thermocouple
combinations which can be made, the world has standardized
seven types which exhibit a range of desirable features. These
thermocouple types are known by a single letter
designation: J, K, T, E, R, S or B. While the composition of
these thermocouples are international standards, the color
codes of the wires are not. For example, in the USA, the

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negative lead is always red, while the rest of the world uses
red to designate the positive lead. Often, the standard
thermocouple types are referred to by their trade names. For
example, K-type is sometimes called Chromel-Alumel, which
is the trade name of the Ni-Cr and Ni-Al wire alloys.

It is important for a good thermocouple to have a large, stable
Seebeck coefficient, wide temperature range, corrosion
resistance, etc. Generally, each wire of the thermocouple is an
alloy. Variations in the alloy composition and the condition of
the junction between the wires are sources of error in
temperature measurements. The standard error of
thermocouple wire varies from ±0.8 °C to ±4.4 °C, depending
on the type of thermocouple used.

Voltage vs. temperature measurements have been tabulated by
NIST for each of the seven standard thermocouple types.
These tables are stored in the read-only memory of the SR630.
The instrument operates by converting a voltage measurement
to a temperature, with the internal microprocessor
interpolating to achieve 0.1 °C resolution.

The K-type thermocouple is recommended for most general
purpose applications. It offers a wide temperature range, low
standard error, and has good corrosion resistance. The K-type
thermocouples provided by SRS have a standard error of
±1.1 °Chalf the standard error designated for this type.

SR630 Thermocouple Monitor

Type B E J K R S T

Positive Material Pt/Rh (30 %) Ni/Cr Fe Ni/Cr Pt/Rh (13 %) Pt/Rh (10 %) Cu
Negative Material Pt/Rh (6 %) Cu/Ni Cu/Ni Ni/Al Pt Pt Cu/Ni
Positive Color (USA) Grey Purple White Yellow Black Black Blue
Negative Color (USA) Red Red Red Red Red Red Red
Lowest Temperature 50 °C −200 °C 0 °C −200 °C 0 °C 0 °C −200 °C
Highest Temperature 1700 °C 900 °C 750 °C 1250 °C 1450 °C 1450 °C 350 °C
Minimum Std. Error ±4.4 °C ±1.7 °C ±2.2 °C ±2.2 °C ±1.4 °C ±1.4 °C ±0.8 °C

Figure 4: Thermocouple reference data