BF5 User Manual v
2.
3
Introduction
13
4. Power from the PC’s serial port (but not some laptops). The BF5
draws power from the PC DTR signal. Most computer serial ports will
provide enough power for the BF5 sensor electronics (but not its
heater).
If more than one of these sources is present, then power is generally
taken from the source with the highest voltage.
If no alkaline batteries are fitted, the power supply must be capable of >5V
at 2mA.
To prevent power being drawn from the data logger include a 10k resistor
in the logger power cable. This is OK as long as power is available from
elsewhere, e.g. from the heater supply
See also the
BF5 Quick Start Guide
.
Heater
The BF5 is fitted with an internal thermostatically controlled heater for
protection against frost and condensation. The heater is mounted on the
shadow mask, which will transfer heat around the inside of the dome and
the top of the enclosure.
When power is applied to the heater supply cables, it works as follows:-
The heater current is controlled by a 8 Hz pulse-width modulated
switch.
If the external temperature is below 0
C, the heater provides the full
power available (up to 20W at 15V).
Above 0°C, the power reduces smoothly to 20% at 5
C, and then
down to nothing at 33°C.
Heater control
0
10
20
30
40
50
60
70
80
90
100
-10
-5
0
5
10
15
20
25
30
35
40
Temp degC
H
ea
te
r
C
u
rr
en
t
%