WIKA CER6000 Operating Manual

Advantages of

Calibration
technology

AC

resistance

thermometry bridges

Resistance thermometry bridges

By using internal or external standard resistors (model CER6000), resistance thermometry bridges measure resistance ratios
with high accuracy, which are indicative of the temperature, among other things. Due to their high accuracy, these instruments

are not only used in the eld of temperature measurement, but also in electrical laboratories.

ASL equipment is used for research, primary and secondary

calibration verication, process monitoring, sterilisation and

validation work by some of the world’s most demanding end
users in the Aerospace, Pharmaceutical, Oil and Gas, Power
and Distribution, Electrical and Electronic industries, and all
International Standards Laboratories including the National
Physical Laboratory in the UK, BIPM in France, PTB in
Germany, NIST in the USA, AIST in Japan and NIM in China.

Our thermometry bridges cover a range of single and multi
channel applications and are used extensively by national

standards laboratories around the world. We oer also high
accuracy precision digital thermometers for scientic and

laboratory use.

Moreover ASL provides a full range Platinum Resistance
Thermometers (PRT) for use in every application from
standards calibration to site temperature measurement. If our

“o the shelf” range will not suit your needs we are able to

supply custom manufactured thermometers to almost any

specication. We also provide a range of Standards Resistors

for use when calibrating Platinum Resistance Thermometers.

2

AC technology

CTR5000

Precision thermometer

Measuring range:

-200 … +962 °C

Accuracy:

0.01, optional 0.005 K

Sensor type:

Pt100, Pt25

Special feature:

Integrated data logger (optional)
Up to 64 channels

Data sheet:

CT 60.20

DC technology

CTR6500 CTR9000

AC resistance thermometry bridge Primary-standard resistance

thermometry bridge

Measuring range:

-200 … +962 °C

Accuracy:

0.1 … 1.25 mK depending on resistance ratio

Sensor type:

SPRT, PRT or xed resistor

Special feature:

Expendable to up to 60 channels (optional)

Internal resistors 25, 100 Ω

AC technology

Data sheet:

CT 60.40

Measuring range:

0 … 260 Ω

Accuracy:

0.1 ppm, 20 ppb optional

Sensor type:

SPRT, PRT or xed resistor

Special feature:

Expendable to up to 60 channels (optional)
4 selectable standby currents possible (optional)
AC technology

Data sheet:

CT 60.80

CTR6000

DC resistance thermometry bridge

Measuring range:

-200 … +962 °C

Accuracy:

± 3 mK (full range)

Sensor type:

PRT, thermistors or xed resistors

Special feature:

Expendable to up to 60 channels (optional)

Internal resistors 25 Ω, 100 Ω, 10 kΩ, 100 kΩ

Data sheet:

CT 60.30

3

Heart of the AC bridge concept

The ratio transformer

The ratio transformer is sometimes referred to as an IVD, an
Inductive Voltage Divider. As suggested by its name the

“simple” task of the ratio transformer is to divide the voltage

across the resistance thermometer R
resistor R
measure the ratio V
R

/ RS.

T

, which carry a common current, and therefore

S

/ VS, which is the same as the ratio

T

and a reference

T

R

S

V

S

Direct Current (DC)

A traditional method for measuring resistance accurately in
this way is the Wheatstone bridge, this is made of two

resistance elements, one of which is xed R

variable R
is the resistance thermometer R
R

. In the Wheatstone bridge, adjustment of the variable

S

resistor R
adjusted to zero. In this condition, when the bridge is said to
be balanced, the ratio R

. As with an AC bridge, the other half of the bridge

V

and the standard resistor

T

allows the voltage across the galvanometer to be

V

/ RF, is the same as RT / RS.

V

and one is

F

R

So the heart of an ASL AC

bridge is a super accurate

voltage divider

However, to help us understand the equivalent AC bridge
principles, it might be easier to picture the Wheatstone bridge
using a decade resistor box to obtain a balance as shown
below.

R

F

T

Decade Box

V

T

R

S

R

T

For our purposes we know RS, so we can calculate RT from RV / RF × R

4

R

R

R

F

S

dc

R

V

R

T

V

S

Alternating Current (AC)

A simplied diagram of an AC bridge is shown below, the

voltage across the standard R
primary winding (P) of the ratio transformer. The secondary
winding (S), or the variable, can be adjusted so the voltage
division is equal to that of R

The secondary winding (S) is far from a simple secondary

and can be shown to take the form of cascaded “decades”,

which can be considered similar in principle to that of the
decade resistor box.

In eect, one tapping of the “unity ratio” decade has ten
tappings which represent “0.1” ratio each. So the AC voltage
across the one unity tapping is also across all ten “0.1” ratio

tappings, hence a division of 10 is available on this AC voltage.

Each “0.1” ratio tapping has ten tappings representing “0.01”

etc.

In this way the ratio of the thermometer R
resistor R
arrangement is shown beside.

may be read directly. A representation of this

S

is measured by the xed

S

to RS.

T

and the standard

T

ac

R

ac

R

R

R

S

T

P S

0-4

0-9

0-9

S

0-9

0-9

0-9

T

Disadvantages of the
DC measurement technique

■ Voltmeter oset and linearity errors

■ Noise on the sense current and voltmeter

■ Sequential measurement temperature change

■ Thermal EMFs

■ Slower speed of response to achieve the correct

measurement

These all lead directly to the measurement uncertainty.

5

Advantages of
the ratio transformer

High accuracy

Accuracy is inherent in the design of ASL bridges, ASL use
AC measurement techniques in its bridges because the
AC ratio technique is the best ratio standard able to provide
higher precision.

Long-term stability

The Ratio transformer (Inductive Voltage Divider) does not
drift with time and has proven to have long term stability
providing consistent measurement results.

Elimination of DC circuit drifts

By using AC the amplier drifts associated with DC

instruments are not a problem, therefore providing good
stability and fast measurements.

Low temperature coecient

The ratio transformer is insensitive to ambient temperature
changes and therefore requires little or no warm-up time
providing less waiting time and no need for ambient
temperature control.

4-wire measurement

To provide the highest possible accuracy and eliminates the

eects of lead resistance within the measurement, even with

the addition of Multiplexers and long cables.

Active input circuitry

Input “guarding” techniques increase the input impedance of
the ratio transformer so as not aect the current and maintain

the measurement accuracy from leakage currents.
This allows the ASL AC bridges to be used in a wide range of

applications without aecting the performance.

Elimination of thermal and
electrochemical EMFs

These eects are cancelled by using AC current, in an

attempt to cancel these errors, DC instruments reverse their
measuring current but at the expense of measurement time
and level of accuracy.

DC instruments have to reverse their measurement current
periodically in an attempt to match the AC bridge perfor­mance and in doing so extend the measurement time. In

eect, DC measurements are sequential, whereas AC bridge

measurement is concurrent, or overlapping, so there are no
errors caused by conditions changing while the actual
measurement is taking place. In addition these current
reversals in DC instruments generate heating and cooling

due to the Peltier eect at all the connections in the meas­urement circuit. This heating and cooling eect then caused

thermal EMFs to be created and will be added to the
thermometer voltage, even when reversed the measure
resistance will be higher than the true ohmic value.
By contrast the low frequency AC measurement technique

will not allow time for signicant heating and cooling to take

place, so the true ohmic value of the thermometer is
measured.

Low frequency carrier

The use of 25 ... 75 Hz (30 ... 90 Hz) almost completely

eliminates the “1/F noise” generated within DC instruments,

this provides a measurement that is more precise, has lower
noise, a high resolution and in a fast time.

The “1/F noise” or “icker noise” is basically the tendency of
the oset voltage of many meters and ampliers to vary

erratically in a way which is inversely proportional to
frequency. With the CTR9000 (ASL F900 / F18) a matching
transformer is part of the design that optimally matches the

Thermometer resistance that also reduces the eects of

noise at this level of measurement.

This measurement frequency also provides an inherent
rejection of line / supply frequency interference and

harmonics, while reducing reactive eects with a quadrature

servo enabling the correct resistance values being obtained
in the measurement.

6

With important criteria to the

right product

Model

CTR5000

CTR6000 ○

CTR6500

CTR9000

Legend  possible ○ not possible

Technology Accuracy Reference resistors Sensor current

AC DC Full range Internal External Standard User Maximun







○ 0,005 K



○ 1 ppm

○ 20 ppb ○

3 ppm



   

   

○

  



○ 64

Number of

channels

60

60

60

Industries

Our temperature measuring bridges are mainly used to measure and calibrate temperature sensors. Our products make your
measurements and calibrations very easy. This is ensured through intuitive operation and very precise measurement
technology.

Automotive industry

Calibration of high-precision automotive sensors and
transmitters.

Heating, ventilation, air-conditioning

Accurate measurements for applications such as
air-conditioning, water heating and cooling systems.

Manufacturing of temperature sensors

Measurement of process-critical parameters during
manufacture.

WIKA and ASL

ASL (Automatic Systems Laboratories) is a worldwide leader
in the manufacture of temperature products in the area
covering high-precision temperature hand-helds through to
the highest level of temperature measuring bridges.

Pharmaceutical industry

Precise calibration of measuring systems from production in
the manufacture of medical instruments, surgical equipment
and of innovative medical solutions.

Oil & gas

Precise calibration for instruments in harsh, dirty
environments.

Calibration service

Ecient and precise calibration conforming to local and

national standards.

Since 2013, ASL has been part of the WIKA Group in the
calibration technology division. Since then, ASL has improved

even further. Modern and ecient warehousing ensures short

and exact delivery times.
The services and product range will be expanded even further.

7

Accessories

CTP5000-T25

High Precision Standard Platinum
Resistance Thermometer (SPRT)

Measuring range:

-189 … +660 °C

Sensor type:

Pt25

Dimensions:

d = 7 mm, l = 480 mm

Special feature:

Free cable ends,
DIN or SMART connector

Data sheet:

CT 61.20

CER6000-RW

Standard reference resistor

Resistance value:

1, 10, 25, 100, 300, 400, 500, 1,000 and

10,000 Ω

Long-term stability:

2 ppm per year
(HS version 0.5 ppm per year)

Special feature:

Low temperature coecient

Rugged stainless steel construction

Data sheet:

CT 70.30

Highest precision
for each requirement

In addition to the umbrella brand WIKA, you will also nd the

brand ASL for the measurement parameter temperature.
With these established brands within the calibration market
we deliver the ideal solution for each measurement task.

The products of ASL can be combined perfectly with the
WIKA product programme, even allowing a presentation to
the most exigent customers, as a full-range supplier.

Range of services

Measuring range: -200 … +1,300 °C
Control range: -55 … +1,100 °C

WIKA Alexander Wiegand SE & Co. KG

Alexander-Wiegand-Straße 30 / 63911 Klingenberg/Germany
Tel. [phone] / Fax [phone]
[e-mail] / www.wika.de

14113518 02/2016 EN