HMP45C212 TEMPERATURE AND RH PROBE
3
TABLE 1. Datalogger Connections for Single-Ended Measurements
Description
Colour
CR10(X), CR500
CR23X
21X, CR7
Temperature
Orange
Single-Ended Input
Single-Ended Input
Single-Ended Input
Relative Humidity
Green
Single-Ended Input
Single-Ended Input
Single-Ended Input
Temperature Signal
Reference
White
AG
Power Control
Yellow
Control Port
Control Port
Control Port
Power
Red
12 V
12 V
12 V
Power Ground
Purple
AG
Shield Clear
G
Temperature Excitation
Black
Switched Excitation
Switched Excitation
Switched Excitation
5. WIRING
Connections to the datalogger for the HMP45C212
are shown in Figure 3 and Table 1. The probe
requires two single ended analog measurements,
the green (RH) and the orange (temp.) leads can
be inserted into either HI or LO inputs.
The black thermistor excitation lead connects to
any excitation channel. The yellow lead is used to
control switching 12 volts to the relative humidity
sensor and is connected to a control port. The
number of HMP45C212 probes per excitation
channel is physically limited by the number of lead
wires that can be inserted into a single excitation
terminal (approximately 10).
The white lead connects to Analog ground.
Analog ground, labelled “AG” on the CR10X, is the
same as Ground (G) for the 21X and CR7. The
clear lead is the shield which connects to Ground
(G) on the datalogger.
6. PROGRAMMING
Program Instruction 4 is used to measure the
temperature.
Program Instruction 4 sets an excitation voltage to
the thermistor bridge then makes a single ended
voltage measurement. The thermistor portion of
the probe has a linear millivolt output over the –50
to +50 Celsius range. A multiplier of 0.07154 and
an offset of –72.789 provides output of
temperature in Celsius.
The HMP45C212 output scale is 0 to 1000
millivolts for the relative humidity range of 0 to
100%. On the RH measurement, use a multiplier
of 0.1 for percent and a multiplier of 0.001 for
fraction output. The RH measurement does not
require an offset.
Example 1. Sample CR10(X) Program Using Single-Ended Measurement Instructions
;Measure the HMP45C212 temperature.
;
01: P
4
Excite, Delay, Volt (SE)
1: 1 Rep
2:
5
2500 mV Slow Range
; CR510 (2500mV); CR23X, 21X, CR7 (5000mV)
3:
3
IN Chan
; Orange Wire (SE3)
4: 1 EX
Chan
5: 0 Delay
6:
2500 mV
Excitation
7:
1
Loc [Air Temp.]
8: .07154
Mult
;
Degrees
Celsius
9: -72.789
Offset
;
Degrees
Celsius
;Turn the HMP45C212 RH circuitry on.
;
02: Do
(P86)
1:
41
Set Port 1 High
; Yellow wire (C1)
