DS9101 datasheet(19/55 Pages) MAXIM

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During a mission, if humidity logging is enabled, the

HRH byte (H11 to H4) is always recorded. The HRL

byte is only recorded if the DS1923 is set up for 16-bit

humidity logging. The logging mode (8-bit or 16-bit) is

selected through the HLFS bit at the Mission Control

With HRH and HRL representing the decimal equivalent

of a humidity reading, the actual humidity is calculated

according to the algorithms shown in the table below.

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

______________________________________________________________________________________

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BYTE

020Eh

HRL

020Fh

H11

H10

HRH

16-BIT MODE, HLFS = 1

8-BIT MODE, HLFS = 0

IVAL = (HRH x 256 + HRL)/16

Round IVAL down to the nearest integer; this eliminates the

undefined 4 bits of HRL.

(N/A)

ADVAL = IVAL x 5.02/4096

ADVAL = HRH x 5.02/256

HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307

Table 3. Humidity Conversion Examples

HRH

HRL

MODE

HEX

DECIMAL

HEX

DECIMAL

HUMIDITY (%RH)

8-bit

B5h

181

84.41

8-bit

67h

103

34.59

16-bit

B5h

181

C0h

84.89

16-bit

67h

103

30h

34.70

Table 4. Humidity Alarm Threshold Examples

HALM

HUMIDITY (%RH)

HEX

DECIMAL

97h

151

58h

Latest Humidity Conversion Result Register Bitmap

The result is a raw humidity reading that needs to be

corrected to achieve the specified accuracy. See the

Software Correction Algorithm for Humidity section for

further details.

To specify the humidity alarm thresholds, the equation

needs to be resolved to:

ADVAL = HUMIDITY(%RH) x 0.0307 + 0.958

HALM = ADVAL x 256/5.02

Round HALM to the nearest integer.

The HALM value needs to be converted into hexadeci-

mal before it can be written to one of the Humidity Alarm

Threshold registers (Low Alarm address 020Ah; High

Alarm address 020Bh). Independent of the conversion

mode (8-bit or 16-bit), only the most significant byte of a

humidity conversion is used to determine whether an

alarm is generated. The alarm thresholds are applied to

the raw humidity readings. Therefore, if software correc-

tion is used, the effect of the software correction is to be

reversed before calculating a humidity alarm threshold.

For example, let the desired alarm threshold be 60%RH.

The 60% threshold may correspond to a raw reading of

65%RH (i.e., before correction). To set a 60%RH (after

correction) threshold, the HALM value then needs to be

calculated for 65%RH.

These examples do not include the effects of software

correction.

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