Greisinger GMH 3750 Digital Thermometer 601866 Benutzerhandbuch

H49.0.02.6C-06

Operating Manual GMH 3750

Page 14 of 16

The device is very precise (please refer to technical data). To be able to use this high precision, the connected
temperature probe has to be as precise as possible, too. The following precision classes are available as a standard at
reasonable prices (Platinum resistor thermometers according to EN60751):

  ± (0,03 + 0,0005 • | Temperature |)

 

0

1

2

3

4

-200

-100

0

100

200

300

400

500

600

700

800

B

1/3B

1/10B

A

GMH37xx

0

0,2

0,4

0,6

0,8

1

1,2

-50

0

50

100

150

B
1/3B
1/10B
A
GMH37xx

For applications demanding higher precision than given by this classes we suggest to adjust the device to the used
probe or to get a calibration certificate for the device combined with the probe.
Attention: if an adjusted or calibrated probe is replaced, also the adjustment or calibration certificate has to be renewed
to maintain the referring overall precision! Be careful when buying third party temperature probes: Besides the standard
EN60751 there are some other obsolete or unusual standards on the market. If such a probe has to be connected, the
user sensor curve (have a look to the referring chapter) can be used to adjust the instrument!

When using resistance thermometers as the Pt100 a quite large measuring error can be caused by inadequate cables
and connections. Using 4wire measuring avoids this kinds of errors mainly caused by unwanted resistances. It is
suggested to use suitable probes and extensions only. (For pin assignment please refer to chapter 7)

Especially when measuring temperatures which deviate very much from the ambient temperature, measuring errors
often occur if the heat loss caused by the probe is not considered. When measuring fluids therefore the probe should be
emerged sufficiently deep and be stirred continuously. When measuring gases the probe should also emerge as deep
as possible in the gas to be measured (e.g. when measuring in channel/pipes) and the gas should flow around the probe
at sufficient flow.

If temperature of the surface of an object has to be measured, one should pay attention especially when measuring hot
(or very cold) surfaces, that the ambient air cools (or heats) the surface. Additionally the object will be cooled (or heated)
by the probe or the probe can have a better heat flow to the ambient temperature as  to the objects surface.
Therefore specially designed surface probes  should be used. The measuring precision depends mainly on he
construction of the probe and of the physics of the surface itself. If selecting a probe try to choose one with low mass
and heat flow from sensor to handle. Thermally conductive paste can increase the precision in some cases.

Pt100 Sensors are defined over a wide temperature range. Depending on probe materials and sort of sensor (e.g. hybrid
sensors, wire wound resistors...) the allowable temperature ranges have to be considered. Exceeding the ranges at
least causes a wrong measuring, it may even damage the probe permanently!
Often it also has to be considered, that the temperature range is just valid for the probe tube, (plastic-) handles can’t
stand the same high temperatures. Therefore the tube length should be selected long enough, that temperature keeps
low at the handle.

The measuring current of the instrument is just 0.3mA. Because of this comparably low current practically now self
heating effect has to be considered, even at air with low movement the self heating is <= 0.01°C.

When measuring air temperature the probe has to be dry. Otherwise the cooling due to the evaporation causes too low
measuring.