ROTRONIC HP21 - Manual (Page 9)

E-M-HP21-V1_21
Rotronic AG
Bassersdorf, Switzerland
Document code Unit
HygroPalm HP21 hand-held indicator:
User Guide Instruction Manual
Document Type
Page 9 of 14
Document title
© 2009-2010; Rotronic AG E-M-HP21-V1_21
The optional HW4 software can also be used to change the unit system:
4.6 Low battery indicator
When the battery is down to about 20% of its initial charge, “Low Battery” appears at the bottom of the display.
4.7 Practical advice for measuring humidity
The most common source of error when measuring relative humidity is a difference between the
temperature of the probe and the temperature of the environment. At a humidity condition of 50 %RH, a
temperature difference of 1 C (1.8 F) typically results in an error of 3 %RH on relative humidity.
When using the HP21 hand-held indicator, it is good practice to monitor the display for temperature
stability. The probe should be given sufficient time to equilibrate with the environment to be measured. The
larger the initial temperature difference between the probe and the environment to be measured, the more
time temperature equilibration requires. This time can be shortened, and errors avoided, by using the probe
configuration that fits best for your application.
In extreme situations, condensation may occur on the sensors when the probe is colder than the
environment. As long as the humidity / temperature limits of the humidity sensor are not exceeded,
condensation does not alter the calibration of the sensor. However, the sensor has to dry out before it can
provide a valid measurement.
Non-moving air is an excellent insulator. When there is no air movement, surprising differences in temperature
and humidity can noted over short distances. Air movement at the probe generally results in measurements
that are both faster and more accurate.
5 Maintenance
5.1 Service cable
Cable AC3006 converts UART (service connector) to USB and is used to connect the HP21 to a USB port
of a PC running the ROTRONIC HW4 software. Prior to using this cable, the ROTRONIC USB driver must
be installed on the PC. Both the driver and the installation instructions (document E-M-HW4v3-Main) are
located on the HW4 CD.
As an alternative, cable AC2001 is used to connect the HP21 to a probe input of the HP23 hand-held
calibrator. For service purposes, the HP23 offers essentially the same functionality as the HW4 software.
5.2 Location of the service connector (mini USB type)
WARNING: the service connector is a UART
interface with a mini-USB connector type. Do not
connect the service connector directly to the USB
port of a PC or hub.
The service connector (UART interface) can be
accessed without opening the enclosure after
removing the protective red round cover.