Vaisala PTU200 Series User's Guide download pdf (Page 43)

CHAPTER 6_______________________________________________ CALIBRATION AND ADJUSTMENT

VAISALA _________________________________________________________________________ 39

As the D (dry) and W (wet) adjustments may affect each other, check

again the humidity reading at the low end. If needed repeat the

procedure in low and high ends until the reading is correct.

Temperature

The temperature channels of PTU200 transmitters are very stable and

the probes have been calibrated and adjusted at the factory. Unless

there is a strong reason to believe that the adjustments have changed,

DO NOT perform a temperature adjustment. This is a very demanding

procedure and requires extremely accurate references. Furthermore, it

is important to allow enough time for the stabilization during

calibration. If for some reason, it is necessary to perform the

temperature adjustment, follow attentively the instructions given

below.

NOTE

The temperature channel has to be calibrated if the probe head has

been changed.

The temperature adjustment can be done via the serial line using linear

offset and gain corrections. Entering any corrections is protected by

switch SW4. Turn it to write ENABLE position (ON) to be able to

enter new offset and gain corrections.

NOTE

If there is need for an adjustment, check first whether there exist any

previously set corrections. Before entering new corrections, it is

recommended to set the offset to 0 and the gain to 1. Then measure

the temperature again at two reference points, and calculate the new

offset and gain corrections.

Offset

It is recommended to perform the one-point offset correction in

temperature, which is close to average measurement temperature. The

offset can be calculated by using equation 6-1.

measref

TTOffset −= (6-1)

where:

ref

= T measured with an accurate reference thermometer

meas

= T measured with PTU200

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Vaisala PTU200 Series User's Guide Page 43