Isotech PRT Probe Data sheet

Semi-Standard PRTs

Platinum Resistance Thermometers

670°C

to

-50°C

In most industrial laboratories the costly and mechanically fragile SPRT is unnecessary. For these applications the
uncertainties may be larger, and hence the Isotech range of semi-standards may be a more practical choice. Usually
made in stainless steel sheaths 6mm in diameter, with an Ro value of 100Ω and an (R100-R0)/R0 of 0.385. A number of
configurations are available since particular characteristics might be required such as short sensing length, fast response,
or applicability to a particular temperature range.

In this collection of semi-standards Isotech has examined not only the uses that customers put them through but also
the equipment that is used to calibrate them. Most units are now a little longer and have a slightly wider temperature
range than our previous products. The stability of the semi-standard will depend upon its range of usage; your semi­standard should remain within its uncertainties between successive annual calibrations, unless you drop it or otherwise
mechanically shock it. Our semi-standards are now fitted with a handle and strain relief, except where otherwise stated.
All are made with our own high quality 100Ω detectors and completely assembled and calibrated in-house in our UKAS
accredited and supervised Laboratory. Calibration is available with fixed points for the best uncertainties and to give the
highest confidence possible.

Please note that stem conduction accounts for the biggest sources of errors during calibration. Remember that for a
given immersion depth stem conduction is dependent on the temperature difference between the sensing element and
ambient temperature, and on the total conductance of the thermometer assembly. It is sometimes thought (mistakenly)
that a shorter thermometer will be subject to less stem conduction.

Performance

Isotech has generated a long history for many of our
semi-standards. Here are some documented facts:

The 935-14-95 model has the widest temperature
range and consequently is likely to suffer the largest
changes in characteristics.

Guy Snelling sent this email (right) about the 935-14-95.

INDUSTRIAL

Advantages

• Ideal for All Industrial Applications

• High Stability

• Low Drift

• Selection of Temperature Ranges

• Choice of Lengths and Diameters

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Semi-Standards PRTs, continued

Cable

SPECIFICATIONS

Model Number

Diameter (A)

Length (B)

Sensing Length

Handle (C)

Cable (D)

Temperature Range

Application

Features

Annealing Drifts

Handle Length

935-14-61

4mm

300mm

6mm

Yes

2m PTFE
4 wire

-50 to +250°C

Fast Response

Small Stem
Conduction

935-14-13

6mm

350mm

25mm

Yes

2m PTFE
4 wire

-196 to +250°C

Low-Temp. Use

Copper Earth
Screen

935-14-16

6mm

450mm

25mm

Yes

2m PTFE
4 wire

-100 to +450°C

General Use

316 stainless
steel sheath

935-14-72

6mm

375mm

25mm

No

2m PTFE
4 wire

-50 to +670°C

Gemini
Jupiter

Fits lid of
Carry-case

935-14-82

4mm

210mm

6mm

No (Angled)

1.5m PTFE
4 wire

-50 to +250°C

Europa
Venus
Calisto

General
Purpose

935-14-85

6mm

420mm

25mm

No (Angled)

540mm PTFE
4 wire

-50 to +250°C

Oceanus-6

General
Purpose

Diameter

935-14-95

6mm

450mm

25mm

Yes

2mPTFE
4 wire

-100 to +670°C

General Use
Medusa

Metal Alloy
Sheath

INDUSTRIAL

The most severe test of a thermometer is to cycle it from its
minimum temperature of use to its maximum temperature.

Below is tabulated the annealing drifts of a typical 935-14-95.

Annealing Range — 0°C to +670°C

with 4 hour dwell at 670°C

Cycle Number Shift (mK)

1 -0.8

2 -2.2

3 +0.5

4 -0.5

5 -2.3

6 -1.2

7 -0.2

8 +0.6

Total Shift over 8 Cycles: -6.1 mK

Mean Shift per Cycle: -0.76 mK

SPECIFICATIONS — GENERAL

Ro 100Ω ±0.05Ω

Alpha 0.003850 ±0.000005

Stability 0.010 ohm/year

Calibration A NIST Calibration Certificate can be

provided at extra cost

Recommended 1mA
Current

Self-Heating Error 0.004°C
at 1mA

ACCESSORIES

Termination Accessories BW: Bare Wire

TTI: Lemo Connector: suits TTI-5,

TTI-6, and TTI-7
DB: Connector for Dry Block Calibrator
SITE Indicator, or TTI-8

HOW TO ORDER

Please Specify Model Type and Termination Option

(for example 935-14-13/BW)

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