Vaisala HMT360Series - Calculating Current Value Correspondence

Calibration and adjustment____________________________________________________________
Vaisala _________________________________________________________________________ 47
1. Connect with banana plugs a power supply (12...24 VDC, with a serial port the
minimum supply voltage is 15 VDC ) to the terminals B1(-) and C1(+) (channel 1), see
Figure 9-2.
2. Connect the multimeter in series with the supply, B1(-) and A1(+).
3. Follow the same procedure with channel 2 using the terminals B2 (-) and C2 (+). When
calibrating both channels at the same time, use two galvanically separated power
supplies.
You can now calibrate or check the humidity and temperature or the analog outputs
according to the instructions given in calibration chapters.
If the current measurement is needed in a hazardous area, the multimeter is connected to the
terminals A1/A2 (+) and B1/B2 (-). Use only an approved multimeter.
WARNING
The power supply connectors (C1 and C2) MUST NOT be used in hazardous
areas. For calibration in a hazardous area use only an approved multimeter,
which fulfils the safety factors printed on the protective cover.
Calculating the correspondence of current
values and output quantities
When using HMT360 without a display, calibration is carried out by using a multimeter.
Use the following equations to calculate the current values corresponding the reference
output quantities.
min)max(
min)(
164
QQ
QQref
mAmAI
−
−
⋅+= (9-1)
where: Qref = reference value of the calibrated quantity
Qmin = value corresponding to 4 mA
Qmax = value corresponding to 20 mA
Example 1:
relative humidity scaling 0 - 100 %RH, reference 11.3 %RH:
mA
RHRH
RHRH
mAmAI 808.5
)%0%100(
)%0%3.11(
164 =
−
−
⋅+=
Example 2:
temperature scaling -40 - +120 °C, reference 22.3 °C
mA
CC
CC
mAmAI 230.10
)40120(
)403.22(
164 =
°−−°
°−−°
⋅+=