Testo 6651, 6681 Data sheet

Industrial Measurement Transmitters for Critical
Climate

NEW!

testo 6651
testo 6681

%RH

°C/°F

°C

td

°F

td

g/m

3

g/kg

J/g

hPa

Committing to the future

2

The basis of stability - the Testo humidity sensor

The Testo humdity sensor: the central component of
high-quality humidity measurement transmitters

For years, Testo has been the first choice when it comes
to high-quality measurement transmitters for drying
processes and critical climate.

On the basis of our years of experience, the sensor and
signal processing concept has been completely
reworked.

Whether high humidity, corrosive media or constant
cleanroom conditions: the Testo humidity measurement
transmitters testo 6651 and testo 6681 offer optimum
accuracy and long-term stability.

Inter-laboratory test

Every specialist around the world knows and values it - the Testo
inter-laboratory test. With it, Testo has impressively proven that very
different national calibration laboratories (with their widely differing test
procedures), have confirmed the Testo humidity sensor’s highest
accuracy.

What exactly happened? After five years travelling around the world,
the Testo humidity sensors, which had been exposed to very different
loads, all showed accuracies of better than ±1 %RH!

This would already be an excellent result for a single test! With regard
to a time series of five years, it testifies to a quality which is of highest
priority to all users worldwide: first class long-term stability!

Long-term stable, condensation-proof and based on
international standards (ILAC / PTB / NIST etc.): the Testo
humidity sensor

Upper electrode

Lower electrode

Carrier

Connections

Dielectric layer

Polymer, constantly alters alters

permeability with the relative

humidity

Allows moisture to

penetrate through to the

dielectric layer and protects

from contamination

Ceramic substrate for
mechanical protection

Special anti-corrosive

design

5 10721346 98

Germany

PTB

04/96

08/96

France

CETIAT

10/96

10/96

USA

NIST

12/96

05/97

Italy

IMGC

07/97

10/97

England

NPL

09/98

09/98

Spain

INTA

10/98

10/98

Japan

JQA

03/99

04/00

Korea

KRISS

05/00

09/00

China

NRCCRM

10/00

12/00

Germany

PTB

03/01

08/01

Country

Institute

Arrival

Departure

International 5-year inter-laboratory
test of the Testo humidity sensor

3

The basis of stability - the Testo humidity sensor

High humidity measurement - testo 6614

Humidity measurement in the high humidity range is
among the most difficult mesasurement tasks. Unstable
measurement values, delayed signal reaction, and
sometimes also sensor corrosion are no rarity, if a special
solution is not used

For these applications, Testo has developed a special,
heated humidity sensor with the testo 6614. A
microclimate which is 5 Kelvin above the process
conditions is thus created inside the filter. The
considerably lower humidity in the microclimate greatly
improves the sensor reaction as well as noticeably
reducing the likelihood of corrosion.

Parallel to the heated humidity sensor, the testo 6614
also has an additional temperature probe. This measures
the actual process temperature; on this basis the correct
process humidity is calculated in the microprocessor of
the measurement transmitter, and displayed.

Trace humidity measurement - testo 6615

Humidity measurement in the lowest humidity range is
also very demanding. If “normal” polymer humidity
sensors are used here, the error, measured in dewpoint
degrees, soon shows high values.

For the demanding measurement of trace humidity, Testo
has developed the testo 6615, which has an integrated
trace humidity self-adjustment. The smallest
discrepencies are corrected cyclically here, up to trace
humidities of -60° dewpoint!

Humidity measurement in corrosive media –
testo 6617

Humidity measurement in corrosive media is often
accompanied by a short useful life of the sensor. For this
problem too, Testo has developed a ground-breaking
innovation: cover electrode monitoring.

Thanks to this measure, the first signs of corrosion are
detected and reported early. This early warning allows the
measurement probe to be exchanged before the
measurement is false or even interrupted. This
guarantees optimum system availability!

4

Overview of the product series testo 6651 and 6681

The two new humidity measurement transmitters from Testo, the
series testo 6651 and testo 6681, are positioned in the middle to
upper performance range. They are designed for the monitoring of
critical climate in process engineering and also in compressed air
technology. The demanding measurement is realized with the further
developed Testo humidity sensor, with its well-known and highly­valued long-term stability. Unmatched state-of-the-art technology in
humidity measurement, with solutions for highest accuracy as well as
for special applications (high humidity, humidity in H

2O2

, trace

humidity etc.) is provided.

Both instrument series present many new features, among them
world innovations such as a professional bus interface in the humidity
measurement transmitter testo 6681

It is a completely newly developed generation of instruments, which in
particular offers solutions for safe and service-friendly use, meaning
high reliability and operational security for industry:

– exchangeable probes

– early warning reports

– variable possibilites for adjustment

In addition, they also continue to use already existing technology such
as the external interface for communication, for example for the
parameterization and adjustment software P2A from Testo.

The overview on the next page shows a comparison of the two
models, followed by a detailed description of the individual models.

Measurement transmitter testo 6681 with and without display

Measurement transmitter testo 6651 with and without display

Measurement transmitter series

5

Overview of the product series testo 6651 and 6681

0 to 100 %RH
(no high humidity processes)

Measuring range Humidity 0 to 100 %RH

5 mmax. cable length 10 m

4 to 20 mA, 2-wire
0/4 to 20 mA, 4-wire
0 to 1/5/10 Volt, 4-wire

Signal outputs 4 to 20 mA, 2-wire (not for testo 6614/6615)

0/4 to 20 mA, 4-wire
0 to 1/5/10 Volt, 4-wire

ABS, plastic, IP65Housing Metal, IP65

digital Testo (for P2A software or testo 400/650)Interfaces digital Testo

professional bus (optional intermediary layer

4 relays, optional
early warning system (via display or relay collective
alarm)

Special features Special probe versions for

• Temperature ranges up to +180 °C (+324 °F)

• Trace humidity testo 6615

• High humidity testo 6614

• Self-diagnosis testo 6617
4 relays, optional
early warning system (via display, relay collective alarm
or professional bus)

Wall probe testo 6601
Duct probe testo 6602/6603
Cable probe testo 6604/6605

Mounting variants Wall probe testo 6611

Duct probe testo 6612
Cable probe testo 6613/6614/6615/6617

-20 to +120 °CTemperature

(dependent on probe)

-20 to +180 °C

±(1,7 %RH + 0,007 x mv)Accuracy at

+25 °C (+77 °F)*

Humidity up to ±(1 %RH + 0,007 x mv)

Pt100 Class A
±0,2 °C / 0,38 °F

Temperature* Pt100 1/3 Class B

±0,15 °C / 0,27 °F

°C/°F, %rF/%RH, °C

td

/°F

td

Measurement parameters

°C/°F, %rF/%RH, °C

td

/°Ftd,°C

tpd

/°F

tpd

, g/m3/gr/ft3,

g/kg/gr/lb, enthalpy/°Ctw, °Ftw, inch, H

2

O, ppm(vol),

% Vol

Probe 6615 only: °C

tpd

/°F

tpd

for H2O2-applications: °Ctm/°Ftm

testo 6651 testo 6681

*Other accuracies apply for the wall probe with 70 mm length in combination with a current output (P07):
Operation: with 2 channels at 12 mA, without display illumination, relay off, additional measurement inaccuracy to above data at +25 °C (+77 °F), humidity ±2.5 %RH,
temperature ±1 °C (1.8 °F)

Price

Performance

testo 6651

testo 6681

Model
Applications

testo 6651

Climate technology and industry:
critical climate, cleanrooms

Industry:
critical climate, cleanrooms, drying processes, high humidity, trace humidity,
humidity in H

2O2

environment etc.

testo 6681

6

P2A software for testo 6651 and testo 6681

Software for parameterization, adjustment and
analysis

Optimum procedures from the point of view of the user –
that is the central idea of the new measurement
transmitter software “P2A” from Testo. The name stands
for

P – Parameterization

A – Adjustment

A – Analysis

All new (and future) Testo measurement transmitters
communicate with this software, the connection of the
PC (via external or easily accessible interfaces) being
extremely easy. The software only needs to be bought
once – all further updates are free of charge!

An additional advantage is the supply of the
measurement transmitter via USB. Parameterization or
analysis can thus be carried out without the need for
wiring – e.g. at a desk or in a workshop.

P2A software: parameterization and data
management

In the course of commissioning, the scaling of the analog
channels, the limit values of the (optional) relays, the
signal damping etc. are set. The P2A software supports
all these procedures with convenient menus which are
extensively supported graphically.

Are several measurement sites intended to have the
same parameters? No problem - the parameter sets can
be transferred by simple “drag and drop”. This saves
considerable time in larger installations.

P2A software: adjustment

In addition to the 1-point adjustment (offset) and the 2­point adjustment (with the help of the saline solution pots
or a humidity generator), the P2A software supports the
analog adjustment of each analog channel. Using a
precise multimeter, the entire measurement chain
(including the digital-analog converter) can thus be
adjusted. Unique: adjustment histories present in detail
who carried out which adjustment when, and at which
reference values. This provides uninterrupted
documentation, independently of whether the
adjustments were carried out with (any) P2A software, the
operating menu or the adjustment buttons.

7

P2A software for testo 6651 and testo 6681

P2A software: analysis and histories

Ideal for the localization of errors and optimization: the
analysis tools of the P2A software. They allow the analog
and relay signals to be tested, and the min./max. values
to be displayed.

How can you look into the past? With the help of an
operational hour counter, the measurement transmitter
stores occuring reoprts with a time stamp. This report
history is displayed in the P2A software and provides
important information on all events.

The P2A software has five such histories.

– Parameterization history (what was set when?)

– Report history (which errors, warnings and status

reports occured)

– History of 1-point adjustments

– History of 2-point adjustments

– History of analog adjustments

As all these procedures are stored in the measurement
transmitter (with operational hour counter), a sound
analysis can be made with the help of any P2A software.

8

Common features + benefits testo 6651 and testo 6681

Display and operating menu

The optional display has an extremely convenient
operating menu. With the help of four operating buttons,
almost all operations can be carried out which can be
conducted using the P2A software. Commissioning,
adjustment and analysis are thus possible completely
without a PC - simply on site!

The display not only presents the measurement values
and relay status clearly, but also guides the user safely
through the operating menu thanks to a clear-text line. A
password protects against unauthorized operation. A
cover for the buttons can also be installed.

And last but not least: The clear-text can be selected in
six languages - optimum for your systems at home and
abroad.

Digital probes

The humidity probe in the models testo 6651 and 6681
can be easily exchanged by hand. A readjustment with
the measurement transmitter itself is not necessary, since
the probe series testo 6600 used in the humidity
measurement transmitter testo 6651 not only has a purely
digital interface to the measurement transmitter, it is also
completely calibrated and adjusted.

Uplug probe 1, plug in probe 2 - continue measuring!

At the same time, Testo fulfils the highest demands, for
example those of the pharmaceutical industry. Each
probe has its own serial number, a store for the
adjustments carried out with it, and its own operational
hour counter. The visualizes (via the measurement
transmitter’s operating menu or the P2A software) how
long the probe has already been in use, and which
settings have been carried out on it (see also P2A
software):

Password (enter if required)

Measurement

operation

Channel 1 Unit channel 1 Select

Scale min. chan. 1 Edit

Scale max. chan. 1 Edit

Signal delay chan. 1 Select

°C

19.3

%RH

57.8

PROBE CONNECTION

9

Common features + benefits testo 6651 and testo 6681

Direct on-site adjustment with the testo 400

A regular adjustment is indispensible for all demanding
humidity measurement - although the highly stable Testo
sensors mean that a correction is often not necesary
even after three or four years.

The important thing for the user is that the process (the
air conditioning system, pasta drying etc.) is not
interrupted by the adjustment procedure. And
transporting a laptop/PC to the measurement site is not
always feasible.

For this reason, Testo has equipped the testo 6651 with
an easily accessible interface. Using the adapter 0554
6022, the reference measuring instrument test 400 or
650 (with a precision humidity probe) can be directly
connected to the measurement transmitter. In the display
of the hand instrument, the humidity and temperature
values of the two instruments are shown opposite each
other. If the discrepancies are too high, a few touches of
a button are sufficient to adjust the testo 6651 (1-point
adjustment). After only a few moments, you are ready to
carry on to the next measurement site.

Adjustment via operating menu or P2A software

In addition to the numerous possibilities for calibrating the
probe together with the measurement transmitter locally,
(cf. P2A software and operating menu), it is possible,
thanks to the digital probe series testo 6600, to leave the
measurement transmitter on site and to exchange only
the probe and calibrate it in a laboratory.

Companies with internal calibration laboratories install at
least one testo 6651 measurement transmitter in the
laboratory and use it as an adjustment basis for various
probes. After adjustment, the probes - or others of the
same design - are reconnected at the original
measurement site. Thanks to the probe serial number, it
is always possible to trace (for example with the P2A
software), which probe was connected when to a
measurement transmitter, and how it was adjusted (1 or
2-point adjustment).

Measurement transmitter and probe

Humidity generator

1-point adjustment on site with the portable instrument testo 400 or testo
650 with precision humidity probe and adjustment adapter

Adjustment via operating menu or testo P2A software

testo 400
testo 650

USB to Mini DIN

cable

Adjustment adapter

10

testo 6651 – features + benefits

Designed for practice

The emphasis in the construction of testo 6651 and testo
6681 was practicability. Here a few examples:

– Adjustment buttons, test points (see below) and

interface should be easily accessible for the specialist,
but not for others. This was the reason for designing
the “

service ccover

” which frames the display.

–

Test ppoints

: do the analog outputs need to be tested
when commissioning the instrument? Are analog
adjustments to be made at a later date? Instead of
disconnecting already existing wiring (and opening the
housing), test points (see photo at left, e.g.
Ch.1+/Ch.1-) were positioned under the service cover,
which allow easy access to the analog signals.

–

Wiring ccompartment

: Which practician is not often
frustrated by the minimal space afforded by
measurement transmitter manufacturers for wiring? For
this reason, Testo has designed a separate wiring
compartment with plenty of space. The practician will
appreciate it.

Duct version with exchangeable probe

For many users, the duct version, in which the probe is
classically attached to the rear wall of the measurement
transmitter, is the best solution. The measurement
transmitter must not be mounted separately, but is held in
position by the probe (1).

With the testo 6602/6603 (for testo 6651) as well as the
testo 6612 (for testo 6681), Testo has succeeded in
making this version available for the first time on the world
market for exchangeable digital probes. The intelligent
probe-cable construction means that the measurement
transmitter is simply pushed ove the end of the probe (2),
and the digital probe plug is then plugged in (3).

11

!

testo 6651 – features + benefits

Integrated relays (optional)

Thanks to the four power relays (up to 256 VAC, 3A),
assemblies of the air conditioning system can be directly
switched without the “detour” via a control. At the same
time, the relays can be used for local alarming or for
reporting limit value violations to a superordinate system.

And not least, the person responsible for the system can
be called to the measurement site in time with the help of
a “collective alarm” (cf. self-monitoring”).

Self-monitoring

The testo 6651 constantly monitors itself: its voltage
supply, when 100 %RH is reached, any drift in 2-point
adjustment etc.

The reports resulting from this are not only stored with an
operational hours stamp - for later analysis - and shown
in the display!

With the help of the optional relays, these reports can
also be given out as a “collective alarm”. The person
responsible - working as a team with the testo 6651 - can
thus always ensure optimum system availability!

R1 R2

R4R3

°C

%RH

12

testo 6651 – the humidity measurement transmitter for critical climate applications

Not all measurement problems in air conditioning technology can be
solved with “simple” measurement transmitters like the testo 6621.
Special challenges are mastered by the testo 6651.

– The probe should be digital and exchangeable. In the testo 6651,

even the duct version fulfils this – a world innovation!

– Higher accuracies are required, especially with regard to use over

years

– The humidity parameter dewpoint (°Ctd/°Ftd) is to be used, for

example in processes in which it is of highest priority that the
temperature does not fall below the dewpoint

– Assemblies are to be controlled from the instrument (optional

integrated relays)

– Commisssioning, adjustment and analysis are to be possible

directly in the instrument without software (optional
display/operating menu)

– Changes of parameter, adjustments and reports are to be stored in

the instrument – with operating hour stamp

This and other features make the testo 6651 the first choice for
demanding climate technology, as well as in pasta drying systems,
maturation chambers for charcuterie and similar applications.

Overview of the product range: measurement transmitters testo 6651 and digital probes 6600

Wall Duct Cable

Standard

For

high

humidity

–> heated

For

trace

humidity

–> with

auto-

adjust

Security

–> auto-

diagnosis

at the

sensor

Whether the decision is made in favour of a testo 6651 or a testo 6681 depends above all on the choice of probe, in addition to the
question of the housing material (6681: metal housing), and the humidity parameters or signals to be used (e.g. professional bus only in
testo 6681). In general, the measuring range 0 to 100 %RH applies, although for continuous high humidity the testo 6614 is recommended.

±1 %RH±2 %RH±2 %RH±1 %RH ±1 %RH ±2 %RH

-20 to +120 °C

-20 to +70 °C-20 to +70 °C -20 to +70 °C

-20 to +120 °C

66126611 6613 6614 6615 6617

Probes for testo 6651 (testo 6600)

Probes for testo 6681 (testo 6610)

-40 to +180 °C

-20 to +70 °C

-40 to +180 °C -40 to +180 °C -40 to +180 °C

-60 to +30
°C

tpd

6601 6602 6603 6604 6605

Pasta drying is carried out by measuring humidity

13

14

Order codes measurement transmitter testo 6651

0555 6651 A01 Bxx

B01
B02
B03
B04
B05
B06

C00
C02
C03
C04
C05
C06
C07

K01
K02
K03
K04
K05
K06
K07

D01
D02
D03

H00
H01
H02

F01
F02
F03
F04
F05

G01
G02
G03
G04
G05

4 to 20 mA (2-wire, 24 VDC), not possible with relays
0 to 1 V (4-wire, 24 VAC/DC)
0 to 5 V (4-wire, 24 VAC/DC)
0 to 10 V (4-wire, 24 VAC/DC)
0 to 20 mA (4-wire, 24 VAC/DC)
4 to 20 mA (4-wire, 24 VAC/DC)

Without display
With display / English
With display / German
With display / French
With display / Spanish
With display / Italian
With display / Japanese

Cable input M16 (relay: M20)
Cable input NPT ½”
Cable contact via via M plug connection

%RH / min / max
°C / min / max
°F / min / max
°C

td

/ min / max

°F

td

/ min / max

Clear-text language

not with code “B01”

%RH / min / max
°C / min / max
°F / min / max
°C

td

/ min / max

°F

td

/ min / max

Without relay
4 relay outputs, limit value monitoring
4 relay outputs, limit values channel 1 + collective alarm

IM German-English
IM French-English
IM Spanish-English
IM Italian-English
IM Dutch-English
IM Japanese-English
IM Chinese-English

Cxx Dxx Exx Fxx Gxx Hxx Ixx Jxx Kxx

Channel 1* =

Channel 2* =

The humidity measurement transmitter for critical climate (testo 6651) is generally customer-specifically configured, adjusted and delivered.
Please select the measurement transmitter you require step by step.

Order example measurement transmitter testo 6651

Housing with display with menu in English

4 to 20 mA (2-wire)

Cable input M16/M20

Factory setting channel 1:
%RH with scaling min 0 %, max 100 %*

Factory setting channel 2:
°C with scaling min -10 °C, max 70 °C*

without relay

Instruction manual in German + English

씮

0555 6651 A01 / B01 / C02 / D01 / F01 /
G02 / -10 / +70 / H00 / K01

* The standard scaling is delivered without “min” and “max”

15

Ordering options probe range testo 6600

L01 L02 L03 L04 L05

X––––
–––X–
X–––X
–XXX–
––––X

Ordering pprocedure:
The measurement transmitter and the probes can be ordered independently of each other, (thanks to the digital probe interface), cf order
examples above.
If the measurement transmitter and the probe order are to be assembled together, their order codes are combined in the distribution set 0563
6681

0555 6600 Lxx Mxx

L01
L02
L03
L04
L05

Probe 6601
Probe 6602
Probe 6603
Probe 6604
Probe 6605

M01
M02
M03
M04
M05

Sintered stainless steel filter
Wire mesh protective cap
Sintered Teflon filter
Metal protective cap, open
Plastic cap ABS, open

N00
N01
N02
N05
N23

Without cable (for probe 6601)
Cable length 1 m (for probes 6604/6605)
Cable length 2 m (for probes 6604/6605)
Cable length 5 m (for probe 6605 only)
Cable length, specially for duct versions (for probes 6602/6603)

P07
P14
P20
P28
P50

Probe length 70 mm
Probe length 140 mm
Probe length 200 mm
Probe length 280 mm
Probe length 500 mm

Nxx Pxx

Order example probe

Duct probe (-20 to +70 °C are sufficient)

Sintered stainless steel filter

Probe length 280 mm

씮

0555 6600 L02 / M01 / N23 / P28

16

Technical data measurement transmitter 6651

FURTHER OUTPUTS

ANALOG OUTPUT (uniform for all channels, specify when ordering)

SENSOR (more data see probes)

Housing Plastic

GENERAL

Dimensions 122 x 162 x 77 mm (without probe)

Weight 0.62 kg (without probe)

Display 2-line LCD with clear-text line (optional) and relay status display

Resolution display 0.1 %RH / 0.1 °C

Cable screw fitting M 16 x 1.5 (2x) with inner diameter 4-8 mm

M 20 x 1.5 (2x) with inner diameter 6-12 mm

Probe connection Digital plug-in connection

Voltage supply 2-wire: 24 VDC ±10 %

4-wire: 20 to 30 VAC/DC, 200 mA max. current consumption

Protection class IP 65

EMC 2004/108/EG

Operating temperature housing -40 to +70 °C, with display 0 to +50 °C

Storage temperature -40 to +80 °C

Measurement parameters Temperature in °C / °F

Relative humidity %rF / %RH

Dewpoint in °Ctd/ °F

td

Measurement medium Air, nitrogen, more on request: [e-mail]

Humidity Testo humid. sensor, cap.

Reproduceability better than ±0.5 %RH

Measurement inaccuracy %RH cf. probe data

Reaction time without protective filter

t 90 max. 10 s

-60 to +100 °C

td

or -76 to +212 °F

td

Measuring
range

Humidity

Temperature

Dewpoint

0 to 100 %RH

Probes 6601 6602 6603 6604 6605

-20 to +70 °C -20 to +70 °C -30 to +150 °C -20 to +70 °C -30 to +150 °C

Quantity 2 channels (type analog signal uniform for both channels, specify when ordering)

Relays 4 relays (free allocation to measurement channels or as collective alarm), up to 256 VAC / 3 A, NC/C/NO (optional)

Digital output Mini DIN for Testo P2A parameterization software and Testo portable instruments 400/650 (optional)

Current/accuracy 4 to 20 mA ±0.03 mA (2-wire)

0 to 20 mA ±0.03 mA (4-wire)

4 to 20 mA ±0.03 mA (4-wire) for heated sensor technology

Voltage/accuracy 0 to 1 V ±1.5 mV (4-wire)

0 to 5 V ±7.5 mV (4-wire)

0 to 10 V ±15 mV (4-wire)

Galvanic isolation Galvanic isolation of the output channels (2-wire and 4-wire), isolation of supply from outputs (4-wire)

Resolution 12 bit

Maximum load 2-wire 12 VDC: 100 Ohm

24 VDC: 500 Ohm

30 VDC: 625 Ohm

4-wire 500 Ohm

Accessories testo 6651 see page 26

17

Technical data probe range testo 6600

Model testo 6601 testo 6602 testo 6603 testo 6604 testo 6605

Type Wall

%rF/%RH, °C

td

/°Ftd, °C/°F

Plastic ABS

FEP coated

Plastic ABS

Duct Duct

-30 to +120 °C -20 to +70 °C -30 to +120 °C

Stainless steel

Cable Cable

70/200 mm 280 mm

specially for duct versions

140/280 mm

1/2 m 1/2/5 m

PN 10 (probe tip)
PN 3 (probe end)

200/500 mm

Application

Measurement parameters

0 to 100 %RH

-20 to +70 °C

Measuring range Humidity

Temperature

Material

Measurement
inaccuracy*

Reproduceablility

Probe shaft

Cable

Plug

±(1,7 %RH + 0,007 x mv)Humidity: (+25 °C)

±0.2 °C / 0.38 °FTemperature: at +25 °C / +77 °F

±0.02 %RH/KHumidity: for deviations from

±25 °C

Room climate probe
wall mounting

Climate probe duct
mounting

Process climate
probe duct mounting
for higher process
temperatures

Climate probe with
cable

Stainless steel
process probe with
cable for higher
process temperatures

better than ±0.5 %RHHumidity

Probe
dimensions

12 mmDiameter

Probe shaft length L

Cable length –

without

Pressure tightness

Drawings

Temperature error dependent on process
temperature and electronics temperature

PN 1 (probe tip)

Measurement transmitter

testo 6651

Measurement transmitter

testo 6651

Cable probe

testo 6604/6605

Duct probe

testo 6602/6603

testo
6651

Wall
probe
testo
6601

Process temperature in °C

Measurement inaccuracy in °C

Measurement inaccuracies for %RH of the probe series testo 6600

Measurement value %RH

Measurement inaccuracies in ±%RH

System error 6650 probe, electronics +25 °C
System error 6650 probe, electronics -25 to +70 °C

*Other accuracies apply for the wall probe with 70 mm length in combination with a current output (P07):
Operation: with 2 channels at 12 mA, without display illumination, relay off, additional measurement inaccuracy to above data at +25 °C (+77 °F), humidity ±2.5 %RH,
temperature ±1 °C (1.8 °F)

3,0

2,5

2,0

1,5

1,0

0,5

0,0

0 102030405060708090100

6601, 6602, 6603, 6604, 6605

0,6

0,6

0,5

0,5

0,4

0,4

0,3

0,3

0,2

0,2

0,1

0,1

0

0

-20-10 0 102030 405060708090100110120

-20-10 0 102030 405060708090100110120

-0,1

-0,1

-0,2

-0,2

-0,3

-0,3

-0,4

-0,4

-0,5

-0,5

-0,6

-0,6

18

testo 6681 – the industrial humidity measurement transmitter

Industrial humditiy measurement requires absolute professionalism.
Not only in the running of the system, but also in the measurement
technology used. The industrial humidity measurement transmitter
testo 6681 fulfils the highest demands.
Over and above the features and benefits of the testo 6651 already
described above (digital probes, P2A software etc.), the testo 6681
has a number of additional features, which the practician will
appreciate.
–

Accuracy

, up to ±1 %RH

–

Preventative mmaintenance

via the early warning probe testo 6617

– A number of

humidity pparameters

, such as absolute humidity and

enthalpy etc.

– An absolutely robust

metal hhousing

–A

trace hhumidity

(testo 6615) with auto-adjustment and high

accuracy up to -60 °C

tpd

–A

high hhumidity pprobe

(testo 6614), stable even in continuous high

humidity processes

– The field bus connection via

Profibus-DP

, a world innovation in

humidity measurement
These and other reasons make testo 6681 the first choice in
cleanroom technology, in drying technology, trace humidity and
compressed air processes and demanding air conditioning
technology.

Overview of the product range: measurement transmitters testo 6681 and digital probes 6610

Wall Duct Cable

Standard

Whether the decision is made in favour of a testo 6651 or a testo 6681 depends above all on the choice of probe, in addition to the
question of the housing material (6681: metal housing), and the humidity parameters or signals to be used (e.g. professional bus only in
testo 6681). In general, the measuring range 0 to 100 %RH applies, although for continuous high humidity the testo 6614 is recommended.

±1 %RH±2 %RH±2 %RH±1 %RH ±1 %RH ±2 %RH

For

high

humidity

–> heated

For

trace

humidity

–> with

auto-

adjust

Security

–> auto-

diagnosis

at the

sensor

-20 to +120 °C

-20 to +70 °C-20 to +70 °C -20 to +70 °C

-20 to +120 °C-40 to +180 °C

6601 6602 6603 6604 6605

66126611 6613 6614 6615 6617

Probes for testo 6651 (testo 6600)

Probes for testo 6681 (testo 6610)

-20 to +70 °C

-30 to +150 °C -40 to +180 °C -40 to +180 °C

-60 to +30
°C

tpd

19

testo 6681 – preventive maintenance through early warning

Early warning system and self-monitoring –
preventive maintenance

Today, professional humidity measurement transmitters
are usually reliable links in the humidity regulatory chain.
Testo has made a significant contribution to this with the
help of the robust, condensation-proof Testo humidity
sensor. However, if there are corrosive media in the
process, this often means that after a while the sensor
ceases to function, accompanied by costly rejects (quality
deficiency in the end product) and system downtimes.

Testo has developed a special solution for these
applications: the Testo “early warning humidity probe”
testo 6617. This continuously monitors the Testo humidity
sensor for any symptoms of beginning corrosion. It
recognizes this situation very early. The person
responsible for the system is therefore already warned
before measurement errors or measurement interruptions
occur.

Not only the probe testo 6617 serves as an early warning.
The testo 6681 also has numerous self-analyses, such as

– Warning if a state of condensation exists for too long

– Warning of the suspicion of drift based on the 2-point

adjustment

– Warning of unsuitable operating voltage

How are these early warnings passed on to the
responsible person? In addition to the clear-text display,
one of the four relays can be allocated a “collective
alarm”, and customer-specifically with a selection of
reports, by the P2A software. Additionally, all individual
reports can be transferred, as long as the measurement
transmitter has the digital field bus communication
Profibus-DP, see below.

Thanks to the early warning, the system supervisor can
replace the probe early – and without interrupting the
measurement. The experts know: the costs saved by
such “preventive maintenance” far exceed the
investment.

Continuous measurement thanks to testo 6617

Measurement interruption with conventional humidity probes

%RH Early warning

False measurement

early probe
replacement

Measurement breakdown

... instead of:

The measurement transmitter testo 6681 with duct probe for industrial
application under extreme conditions

20

testo 6681 – the signal outputs

Profibus-DP – finally also for humidity applications

As the first provider of humidity measurement technology
in the world, Testo has made the most common field bus
available: Profibus-DP. This has become standard in
production automation and is also used for drying
processes.

Thanks to an “intermediate layer” (sandwich design), the
testo 6681 can be equipped with this communication
variant ex-works or later on site.

The advantage of the field bus: in addition to the
measurement values, all individual reports (i.e. also the
numerous self-monitoring reports) can be passed on to
the connected control. The relay limit values can also be
altered “from above” (see graphic on left), e.g. to suit the
current production batch.

Analog outputs – two or optionally three

The testo 6681 is also very versatile regarding its analog
outputs. In addition to the type of signal (4 to 20 mA two­wire or four-wire, 0 to 1 V, 0 to 5 V, 0 to 10 V, 0 to 20 mA),
the number of analog outputs can be selected whern
ordering. Two or three channels are available. This
means, for example, that the dewpoint can also be
continuously montored, in addition to the relative humidity
and the temperature, without the need for complicated
calculations in the control.

Integrated relays (optional)

Thanks to the four power relays (up to 256 VAC, 3A),
assemblies of the air conditioning system can be directly
switched without the “detour” via a control. At the same
time, the relays can be used for local alarming or for
reporting limit value violations to a superordinate system.

And not least, the person responsible for the system can
be called to the measurement site in time with the help of
a “collective alarm” (cf. self-monitoring”).

PLC / SCADA / control systems

Digital reports

(limit value violations /

collective alarm)

4 relays

up to 250 VAC

Local
alarm

Assembly
switching

2 / 3 analog outputs

Model testo 6681 with accessory Profibus intermediate layer

(= Profibus-Master)

testo 6681 as “Profibus Slaves”

PLC

21

testo 6681 – high humidity and trace humidity

High humidity – testo 6614

Processes with high humidity are among the most
demanding challenges in measurement technology. In this
range, conventional sensors tend to react slowly, while
corrosion – high humidity processes often contain
corrosive media – can endanger the long-term useability
of the sensor.

Testo provides a unique solution for this application with
the digital probe testo 6614. The sensor heating creates a
highly stable microclimate, in which fast reaction, highly
accurate measurement and corrosion-proofness are
guaranteed. With the help of an additional temperature
probe, the actual process temperature is measured, and
the process humidity calculated in the microprocessor.
Long-term stability with high accuracy – up to now, this
combination was beyond our reach in the high humidity
range.

Trace humidity – testo 6615

Trace humidity – i.e. very low relative humidity or
dewpoint values – is also a very demanding measurement
task. Conventional humidity sensors show their limitations
here, especially in their measurement accuracy.

Testo has now succeeded in developing a special sensor
on the basis of a self-adjustment. With sensational
results: Down to low trace humidities of -60° dewpoint (
this corresponds to a relative humidity of 0.03 %RH at
+25 °C), the digital probe testo 6615 still provides highest
accuracy.

The appropriate accessories for this application are now
also available:

– Prefilter 0554 3311 (for protecting the measurement

chamber and sensor)

– Precision measurement chamber 05544 3312

(stainless steel) with adjustable flow-off, for
measurements in compressed air up to 35 bar

– Flow-through meter for measurement chamber 0554

3313, for monitoring flow-off from the measurement
chamber

With the help of these components, the optimum flow
impact of the sensor, at any pressure (up to 35 bar) and
with optimum contamination protection, can be set. For
long-term stable trace humidity measurements in
compressed air and dry gases.

°C

tpd

Conventional polymer
sensor

Error

Δ °C

tpd

e.g. 73 %RH

Mist

“Microclimate” sensor
conditions after
heating

Process conditions high
humidity

5 K

T

[°C]

[g/kg]

Connection of trace humidity probe testo 6651 via measurement chamber
and protective filter

testo

6615

-60 -30 0 30

22

Order code measurement transmitter testo 6681

0555 6681 A01 Bxx

B01

B02
B03
B04
B05
B06
B77

C00
C02
C03
C04
C05
C06
C07

K01
K02
K03
K04
K05
K06
K07

D01
D02
D03

H00
H01
H02

I00
I01
I02
I03
I04
I05
I06
I07
I08
I09
I10
I11
I12
I13
I14
I15
I16
I17

F01
F02
F03
F04
F05
F06
F07
F08
F09
F10
F11
F12
F13
F14
F15

G01
G02
G03
G04
G05
G06
G07
G08
G09
G10
G11
G12
G13
G14
G15

4 to 20 mA (2-wire, 24 VDC), not possible with relays
or probes testo 6614/6615
0 to 1 V (4-wire, 24 VAC/DC)
0 to 5 V (4-wire, 24 VAC/DC)
0 to 10 V (4-wire, 24 VAC/DC)
0 to 20 mA (4-wire, 24 VAC/DC)
4 to 20 mA (4-wire, 24 VAC/DC)
Profibus-DP

Without display
With display / English
With display / German
With display / French
With display / Spanish
With display / Italian
With display / Japanese

Cable input M16 (relay: M20)
Cable input NPT ½”
Cable contact via via M plug connection

%RH / min / max
°C / min / max
°F / min / max
°C

td

/ min / max

°F

td

/ min / max
g/kg / min / max
gr/lb / min / max
g/m

3

/ min / max

gr/ft

3

/ min / max
ppmV / min / max
°Cwb / min / max (Wet Bulb)
°Fwb / min / max (Wet Bulb)
kJ/kg / min / max (enthalpy)
mbar / min / max (water vapour partial pressure)
inch H

2

O / min / max (water vapour partial pressure)

%RH / min / max
°C / min / max
°F / min / max
°C

td

/ min / max

°F

td

/ min / max
g/kg / min / max
gr/lb / min / max
g/m

3

/ min / max

gr/ft

3

/ min / max
ppmV / min / max
°Cwb / min / max (Wet Bulb)
°Fwb / min / max (Wet Bulb)
kJ/kg / min / max (enthalpy)
mbar / min / max (water vapour partial pressure)
inch H

2

O / min / max (water vapour partial pressure)

Without relay
4 relay outputs, limit value monitoring
4 relay outputs, limit values channel 1 + collective alarm

no optional 3rd analog output
%RH / min / max
°C / min / max
°F / min / max
°C

td

/ min / max

°F

td

/ min / max
g/kg / min / max
gr/lb / min / max
g/m

3

/ min / max

gr/ft

3

/ min / max
ppmV / min / max
°Cwb / min / max (Wet Bulb)
°Fwb / min / max (Wet Bulb)
kJ/kg / min / max (enthalpy)
hPa / min / max (water vapour partial pressure)
inch H

2

O / min / max (water vapour partial pressure)

°Ctm / mixture dewpoint for H

2O2

°Ftm / mixture dewpoint for H2O

2

IM German-English
IM French-English
IM Spanish-English
IM Italian-English
IM Dutch-English
IM Japanese-English
IM Chinese-English

Cxx Dxx Exx Fxx Gxx Hxx Ixx Jxx Kxx

Order example measurement transmitter testo 6681

Housing with display with menu in English

4 to 20 mA (4-wire)

Cable input M16/M20

Factory setting channel 1:
°C

tpd

with scaling min 0 °Ctd, max 100 °Ctd*

Factory setting channel 2:
°C with scaling min -10 °C, max 70 °C*

with relay

without 3rd channel

Instruction manual in Spanish + English

씮

0555 6681 A01 / B06 / C02 / D01 / F04 / 0 / 100 /
G02 / -10 / +70 / H01 / I00 / K03

Clear-text language

* The standard scaling is delivered without “min” and “max”

Channel 3* =

Channel 1* =Channel 2* =

23

Ordering options probe range testo 6610

L11 L12 L13 L14 L15 L17

X–––––
––X–––
XXXXXX
–XX–––
–XXXXX
–XX–––

Ordering pprocedure:
The measurement transmitter and the probes can be ordered independently of each other, (thanks to the digital probe interface), cf order
examples above.
If the measurement transmitter and the probe order are to be assembled together, their order codes are combined in the distribution set 0563
6681

0555 6610 Lxx Mxx

L11
L12
L13
L14
L15
L17

Probe 6611
Probe 6612
Probe 6613
Probe 6614
Probe 6615
Probe 6617

M01
M02
M03
M04
M05
M06
M07
M08

Sintered stainless steel filter
Wire mesh protective cap
Sintered Teflon filter
Metal protective cap, open
Plastic protective cap ABS, open
Teflon filter with drip hole
Teflon filter with drip hole and condensation protection
Filter for H

2O2

environments

N00
N01
N02
N05
N10
N23

Without cable (for probe 6601)
Cable length 1 m (for probes 6604/6605)
Cable length 2 m (for probes 6604/6605)
Cable length 5 m (for probes 6605 only)
Cable length 10 m
Cable length, specially for duct versions (for probe 6612)

P07
P14
P20
P30
P50
P80

Probe length 70 mm
Probe length 140 mm
Probe length 200 mm
Probe length 300 mm
Probe length 500 mm
Probe length 800 mm

Nxx Pxx

Order example probe 6613

Cable probe, -40 to +180 °C

Sintered stainless steel filter

Cable length 2 m

Probe length 300 mm

씮

0555 6610 L13 / M01 / N02 / P30

specially for high humidity

L11 L12 L13 L14 L15 L17

X–––––
–– XXXX
–– XXXX
–– XXXX
–– XXXX
–X––––

24

Technical data measurement transmitter testo 6681

FURTHER OUTPUTS

ANALOG OUTPUT (uniform for all channels, specify when ordering)

SENSOR (more data see probes)

Housing Metal

GENERAL

Dimensions 122 x 162 x 77 mm (without probe)

Weight 1.5 kg (without probe)

Display 2-line LCD with clear-text line (optional) and relay status display

Resolution display 0.1 %RH / 0.1 °C

Cable screw fitting
(Code D01)

M 16 x 1.5 (2x) with inner diameter 4-8 mm

M 20 x 1.5 (2x) with inner diameter 6-12 mm

Probe connection Digital plug-in connection

Voltage supply 2-wire: 24 VDC ±10 %

4-wire: 20 to 30 VAC/DC, 200 mA max. current consumption

Protection class IP 65

EMC 2004/108/EG

Operating temperature housing -40 to +70 °C, with display 0 to +50 °C

Storage temperature -40 to +80 °C

Measurement parameters Dependent on probe, altogether are available:

Temperature in °C / °F; relative humidity %rF (%RH); dewpoint in °C

td

(°Ftd); pressure dewpoint in °C

tpd

(°F

tpd

); absolute humidity in g/m

3

(gr/ft3); degree of humidity in g/kg (gr/lb); enthalpy in kJ/kg (BTU/lb); psychrometer temperature in °Ctw (°Ftw); water vapour partial
pressure in hPa / H

2

O; water content in ppm vol / % Vol; mixture dewpoint H2O2/ in °Ctm / °Ftm

Measurement medium Air, nitrogen, more on request: [e-mail]

Humidity Testo humid. sensor, cap.

Reproduceability better than ±0.5 %RH

Measurement inaccuracy %RH cf. probe data

Reaction time without protective filter

t 90 max. 10 s

Measuring range
(Standard scaling)

%RH °C

td

°F

td

0 to 100 -80 to +100

Measuring
range

Humidity

Temperature

0 to 100 %RH

Probes 6611 6612 6613 6614 6615

-60 to +30 °C

tpd

6617

0 to 100 %RH

-20 to +70 °C -30 to +150 °C -40 to +180 °C -40 to +180 °C -40 to +180 °C -40 to +180 °C

Quantity 2 channels (type analog signal uniform for both channels, specify when ordering)

additional 3rd channel (optional)

Relays 4 relays (free allocation to measurement channels or as collective alarm), up to 256 VAC / 3 A, NC/C/NO (optional)

Digital output Mini DIN for Testo P2A parameterization software and Testo portable instruments 400/650 (optional)

Profibus-DP (optional as an intermediate layer)

Current/accuracy 4 to 20 mA ±0.03 mA (2-wire)

0 to 20 mA ±0.03 mA (4-wire)

4 to 20 mA ±0.03 mA (4-wire) for heated sensor technology

Voltage/accuracy 0 to 1 V ±1.5 mV (4-wire)

0 to 5 V ±7.5 mV (4-wire)

0 to 10 V ±15 mV (4-wire)

Galvanic isolation Galvanic isolation of the output channels (2-wire and 4-wire), isolation of supply from outputs (4-wire)

Resolution 12 bit

Maximum load 2-wire 12 VDC: 100 Ohm

24 VDC: 500 Ohm

30 VDC: 625 Ohm

4-wire 500 Ohm

g/m³

0 to 600

g/kg

0 to 9500

°Cwb °Fwb

Accessories testo 6681 see page 26

-112 to +212 -40 to +180 -40 to +356

25

Technical data probe range testo 6610

Model testo 6611 testo 6612 testo 6613 testo 6614 testo 6615 testo 6617

Type Wall

°C/°F, %rF/%RH, °Ctd/°Ftd, °C

tpd

/°F

tpd

, g/m3/gr/ft3, g/kg/gr/lb, kJ/kg, BTU/lb, °Ctw/°Ftw, hPa, inch H2O, ppm vol %, %vol, °Ctm

(H

2O2

)/°Ftm (H2O2)

Stainless steel

FEP coated

Plastic ABS

Duct Cable

-30 to +150 °C -40 to +180 °C

-60 to +30 °C

tpd

0 to 100 %RH

Heated cable

Cable trace humidity
(self-adjustment)

Cable with cover
electrode monitoring

80/200 mm 200/500 mm

200/300/500/800

mm

specially for duct

versions

PN 10 (probe tip)
PN 3 (probe end)

PN 16 (probe tip) PN 1 (probe tip)

Application

Measurement parameters

0 to 100 %RH

-20 to +70 °C

Measuring range Humidity

Temperature

Material

Measurement
inaccuracy*

Reproduceablility

Probe shaft

Cable

Plug

±(1 %RH + 0,007 x mv) for testo 6611/12/13/14

±(1,2 %RH + 0,007 x mv) for testo 6617

Humidity: (+25 °C)

±0.2 °C / 0.38 °FTemperature: at +25 °C / +77 °F

Pressure dewpopint

±0.02 %RH/KHumidity: for deviations from

±25 °C

Room climate
probe wall
mounting

Process humidity
probe duct
mounting

Process humidity
probe flexible
with cable

Humidity probe for
high humidity
applications / when
risk of condensation

Humiditiy probe for
trace humidity /
pressure dewpoint
(with self­adjustment)

Humidity probe with
self-monitoring for
sensor-damaging
media

better than ±0.5 %RHHumidity

Probe
dimensions

12 mmDiameter

Probe shaft length L

Cable length – 1/2/5/10 m

Pressure tightness

Temperature error dependent on process
temperature and electronics temperature

Measurement inaccuracy in %RH of
the probe sreies 6610

PN 1 (probe tip)

120/200/300/500/

800 mm

Cable probe

testo 6615/6617

Measurement transmitter

testo 6651

Cable probe

testo 6614

Measurement transmitter

testo 6651

Cable probe

testo 6613

Measurement transmitter

testo 6651

Duct probe
testo 6612

testo
6651

Wall
probe
testo
6611

testo 6615/6617testo 6614testo 6613testo 6612testo 6611

Process temperature in °C

Measurement value %RH

Measurement inaccuracy in °C

System error 6680 probe, electronics +25 °C
System error 6680 probe, electronics -25 to +70 °C

testo 6611, 6612, 6613 (under 90% as testo 6614)

testo 6614

testo 6617

±1 K at 0° C

tpd

±2 K at -40° C

tpd

±4 K at -50° C

tpd

Measurement inaccuracy in %RH

Measurement transmitter

testo 6651

*Other accuracies apply for the wall probe with 70 mm length in combination with a current output (P07):
Operation: with 2 channels at 12 mA, without display illumination, relay off, additional measurement inaccuracy to above data at +25 °C (+77 °F), humidity ±2.5 %RH,
temperature ±1 °C (1.8 °F)

3,0

2,5

2,0

1,5

1,0

0,5

0,0

0 1020304050607080 90100

0,6

0,5

0,4

0,3

0,2

0,1

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

0

-0,1

-0,2

-0,3

-0,4

-0,5

-0,6

26

Common accessories testo 6651 and testo 6681

Interface and software Part no.

0554 6020

P2A software (parameterisation, adjustment and analysis software for PC), with USB cable (for PC) to mini DIN (instrument)

Plug connections Part no.

0554 6682

Plug connection M12 5-pin plug and socket

0554 6683

Profibus plug and socket

0554 6688

Profibus end resistance

Accessories for pressure dewpoint measurement (only testo 6681 with probe testo 6615) Part no.

0554 3311

Prefilter, protects measurement chamber and sensor from dirt particles

0554 3312

Precision measurement chamber with adjustable flow-off

0554 3313

Flow-through meter for measurement chamber to adjust specific flow-off of sensor

Fixings, mounting assistance Part no.

0554 6651

Wall/duct holder (for mounting duct version in duct or for mounting duct version on wall)

0554 1793

Basic single hole duct screw fitting in plastic (polyamide, -20...+80 °C), gasket ring in NBR

0554 1794

Duct screw connection (aluminium/PVC)

0554 1795

Pressure-tight screw connection G1/2“ (st. steel) with cutting ring to 10 bar

0554 1796

Pressure-tight screw connection G1/2“ (st. steel) with Teflon ring to 6 bar

0554 1797

Stainless steel flange for screw connections to DIN 2576

Sensor filters and protective caps Part no.

0554 0647

Stainless steel sintered cap, Ø 12 mm, is screwed onto humidity probe
for measurements at high flow velocities or in contaminated air

0554 0757

Cap with wire mesh filter, Ø 12 mm

0554 0756

Teflon sintered filter, Ø 12 mm, for corrosive substances
high humidity range (long-term measurements), high velocities

0554 0755

Metal protection cage, Ø 12 mm for humidity probes
for measurement in flow velocities of less than 10 m/s

0192 0265

Plastic protective cap (open), fast reaction time at flow velocities <7 m/s (not suitable for dusty atmospheres)

0554 9913

Protection cap made of Teflon
With 1.5 mm condensate drip hole

0554 0166

Protection from moisture (aluminium)
Protects sensor from condensation e.g. in drying systems

Adjustment possibilities Part no.

0554 6022

Adjustment adapter (for 1-point adjustment with testo 400 or testo 650)

0554 0660

testo saline pots for control and humidity adjustment of humidity probes, 11.3 %RH and 75.3 %RH with adapter for humidity probe

0699 3556/15

Reference set (testo 650, 1 %RH probe with certificate)

Calibration Part no.

0520 1000

ISO calibration certificate/electrical (for measurement transmitter analog outputs)
calibration in measurement ranges 0 to 20 mA; 4 to 20 mA; 0 to 1 V; 0 to 10 V

0520 1200

Standard DKD calibration, measurement transmitter only

0520 0176

ISO calibration certificate humidity

0520 0066

ISO calibration certificate/humidity
data loggers; calibration points freely selectable from 5 to 95%RH at +15 to +35°C or -18 to +80°C

0520 0276

DKD calibration certificate humidity

0520 0236

DKD calibration certificate/humidity
cal. points freely selectable from 5 to 95%RH at +25° C or +5 to +70°C

Supply Part no.

0554 1748

Mains unit (desk-top) 110 to 240 VAC/24 VDC (350mA)

0554 1749

Mains unit (rail mounting) 90 to 264 VAC/ 24 VDC (2.5A)

27

0981 6214/msp/Si/A/08.2007

· 50 YEARS OF TESTO

INNOVATION 2007

· More innovative than ever

· 50 innovations in the anniversary year

Subject to change without notice.