I've been testing the new HMP155A Temperature and Relative Humidity Probe. The wiring configuration to the CR1000 data logger is as follows:
Yellow - Single ended channel - SE1
Blue - Single ended channel - SE2
White - Signal Ground - AG
Black - Signal Ground - AG
Clear - Power Ground - G
Red - 12 Volts - SW12V
The program code is as follows:
Public AirTC_155
Public RH_155
BeginProg
Scan(5,Sec,1,0)
'HMP155 (Switched power) Temperature & Relative Humidity Sensor measurements AirTC and RH
PortSet (9,1)
Delay (0,150,mSec)
VoltSe(AirTC_155,1,mV2500,1,0,0,_60Hz,0.14,-80)
VoltSe(RH_155,1,mV2500,2,0,0,_60Hz,0.1,0)
PortSet (9,0)
NextScan
EndProg
The Temperature for AirTC_155 is -79.3306.
The RH_155 reading is 48% which is fine.
The temperature reading is out to lunch for this configuration. Why?
When I change red wire from switched 12 vdc to normal 12vdc the AirTC_155 reading is 22.27 C which is fine.
Our recent HMP-45C utilized a control port to power sensor up, delay and then take measurement. This methodolgy worked fine and I would like to use the switched 12 vdc to accomplish if possible. Comments appreciated.
Thanks,
wx2day
Please review the time you are allowing for the sensor to power on. The new generation of "intelligent" sensors take much longer to power on that the older analogue sensors. I would allow at least 3 seconds for that probe.
Thank You, Yes I did find that when I switched the delay time to 2 seconds it worked fine. From earlier posts on the HMP155 I saw where they initially had some issues with delay time for the HMP155. I may too increase it to 3 seconds because at first when comparing an HMP45C to the HMP155A, the temperature was about a degree higher. I'm letting it run overnight to see how it compares. I'll let you know my results Thank You for responding Andrew
wx2day
* Last updated by: wx2day on 3/21/2012 @ 2:58 PM *
Andrew--
A question I have is this at 2 sec delay I noticed the HMP155A compared to the HMP45C was differing by 1 deg Celcius.
When I Changed it to 3 Sec delay it came more in line with the older sensor. What is the purpose for the delay in the program?
wx2day
Your program turns the sensor on and off (you do not have to do this is you have the power). When turned off the on, it takes some while for the microprocessor in the sensor to power up and start giving measurements. This is a second or so. In the case of this sensor the microprocessor makes the measurements and then converts them to an analogue signal. That signal has some filtering on it which means it takes a while for the signal to settle to a final value.
This is why you need to add a delay and it is better not to cut it too short if you want best accuracy under all conditions.