<< Click to Display Table of Contents >> Navigation:  Humidity & Temperature Devices > Probes > PC-Series > PC62 & 62V > Commands for the PC62 Probes

NOTE: Read this carefully - sending commands other than those than stated could damage the device or erase calibration information stored in the probe.

 

 

Programming the Device

When programming the device please ensure that the power supply is as stated in the specifications.

When commands are used to recalibrate the device, precautions should be taken to assure that the

data integrity is guaranteed.

 

 

Addressing

RS485 devices respond to a unique address.

Programming an address into the probe is normally done in the factory but can also be done by the

customer.

It is essential to record an address scheme list. Make sure that every probe on the data bus has a

different address in order to prevent data collision.

A typical program cycle consists of the following command strings:

 

Calibration mode (cmd 0x98)

RH / Temperature / address adjustment command (on next pages)

Make changes permanent in non-volatile memory (Flash) (cmd 0x9F)

Reset command (0xFF) to put probe back into normal operating mode.

 

The commands are explained down below.

 

 

 

Command - ‘Calibration Mode’

For calibration purposes the PC62 has a special mode during which it ceases to give a normal output

and is able to communicate with an external (Master-) device which enables data-exchange.

The probe always expects 5 bytes with ‘STX’ as the starting character and ‘ETX’ as the ending

character. (Without these, the string is not valid and is purged. *)

 

General Data format (always 5 bytes)

 

The command for calibration = ‘0x98’

The value of the 2 data bytes is a safety code (0x44,0x33)

 

Example:

Master sends:

 

After the calibration command, several other commands are valid.

 

Allow 500ms for the probe to finish current tasks and change from normal mode to calibration mode.

 

When the power supply is interrupted the probe will change back to normal operation mode. The

same result can be obtained with the ‘Reset’- command. It has the same format as the calibration

command. The Hex-code for this command = ’0xFF’

 

* ( STX = 0x02; ETX = 0x03 )

 

 

 

Command - ‘Calibrate RH-input’

After the atmosphere in the calibration chamber is stabilized the probe can be (recalibrated. It is a

two- point calibration which involves one calibration in the lower part and one in the higher part of

the measuring range. The probe only needs the two corresponding (reference) values of the Relative

Humidity in the calibration chamber.

 

The calibration cycle for Humidity involves the following commands:

•Send calibration command (0x98)

•Send actual low part Relative Humidity value (coded) to the probe (Cmnd=0x10)

•Send actual high part Relative Humidity value (coded) to the probe (Cmnd=0x11)

•Send Flash ‘program’ command (0x9F)

•Reset probe (Cmnd=0xFF)

 

Calibrating the low part of the RH range:

 

The RH-calibration values are stored with a 0.01 point resolution.

The calibration range for the low part is 5 to 35.50% RH.

The data is stored as a non-signed integer (2753 = 27.53%RH). Likewise the calibration of the high

RH part must take place in the range 70 to 95.5% RH. (Also equivalent to 2 bytes value eg. 78.62%

= 7862 = 0x1E B6 - see example below.)

 

1st cycle: Set calibration mode

 

2nd cycle: Master sends low value Relative Humidity (e.g. 27.53% RH => 2753 = 0x0AC1)

 

3rd cycle: Master sends high value Relative Humidity (e.g. 78.62% RH => 0x1E B6)

 

4th cycle: Program parameters in permanent memory (Flash)

 

 

 

Command - ‘Calibrate Temperature-input’

After the atmosphere in the calibration chamber has stabilized the probe can be calibrated. It is a

one-point calibration at a reference temperature. The probe only needs this (reference) value of the

temperature.

 

There are two calibration methods:

 

1.One-point temperature adjustment at about 23°C.

 

2.Three-point T calibration with two extra (low and high) adjustment points.

 

In order for the probe to show correct data, both the low and high points must be adjusted. A one

point calibration at 23°C is also valid without having to perform a calibration and adjustment on the

other two points. Most probes are delivered with three-point calibration and re-adjusting only one

value is allowed in most cases.

 

The three-point calibration cycle for Temperature involves the following commands:

 

•Set probe to calibration mode (Cmnd=0x98)

•Send actual Temperature value (A-coded) to the probe (Cmnd=0x15) for the mid T-range

•Send actual Temperature value (B-coded) to the probe (Cmnd=0x1B) for the low T-range

•Send actual Temperature value (B-coded) to the probe (Cmnd=0x1C) for the high T-range

•Store parameters in non volatile memory (Cmnd=0x9F)

 

The order of commands 15, 1B and 1C is not important. The only restriction is that whenever

parameters are changed they will not be valid until Command 9F is issued and the probe has been reset.

 

The data at the actual temperature is formatted for degrees Celsius (Centigrade). It is, however,

different for the mid-range adjustment (A-coded versus B-coded).

 

A-coded : The temperature in units of 0.01°C divided over 2 separate bytes:

 

Byte A = the part preceding the decimal point. Byte B = the value after the decimal point (0 to 9).

 

The calibration window for the mid-range temperature is 5 to 35°C.

 

1st cycle: Set probe to calibration mode (see example: ‘Calibration-Mode’)

 

2nd cycle: Send value mid-range T in 0.01° Celsius (e.g. 23.84°C => 23 = 0x17) (84 = 0x54)

 

3rd cycle: Send value low-range T in 0.01° Celsius

Low range adjustment B-coded: The temperature as unsigned integer in units of 0.01°C with an

offset of 40°C (4000) e.g. -18.67°C becomes 2133 ( -1867 + 4000) = 0x08 55.

 

4th cycle: Send value high-range T in 0.01° Celsius

High range adjustment B-coded: The temperature as unsigned integer in units of 0.01°C with an

offset of 40°C (4000) e.g. 55.31°C becomes 9531 (5531 + 4000) = 0x25 3B.

 

5th cycle: Store parameters

 

 

PC62

Command - ‘Request Data’

Probe in normal operation mode

 

Communication parameters:

 

9600 baud, 8 data bits, No parity, 1stopbit

 

Master sends :

 

The Command for requesting data = ’0x1D’

Address: valid bytes = 0x30 to 0x39 and 0x41 to 0x46 (ASCII 0 to 9 - A to F)

 

Example:

0x02 0x1D 0x35 0x37 0x03

 

The reply from the probe is fully ASCII coded.

 

It reads (for example):

Addr =57, RH=46.4%, T=23.1C, Tdew=11.0C, AbsH= 9.6gr/m3

 

 

PC62 with RS485 Protocol

Command - ‘Set New Address’

Probe in Normal / Calibration Mode

Changing the address of the PC62 requires four program cycles : Calibration command; one command

to change the high order part of the address; one for the low order part of the address and a

program Flash command.

 

1st cycle: Set calibration mode (see example: ‘Calibration-Mode’)

 

2nd cycle:

Master sends:

 

3rd cycle:

Master sends :

 

4th cycle: Store new parameters command

The Command for programming new address = ‘0x95’

The identifier works like a pointer to the probe’s ‘non volatile memory’

Address: valid bytes = 0x30 to 0x39 and 0x41 to 0x46 (ASCII 0 to 9 - A to F) *

 

Example: Set new address to ‘0x48’.

 

 

a)Address ‘0xff, 0xff’ is used for RS232 purposes. It changes the probe into a mode with a continuous output of data.

b)It is possible to program the probe with data in the address memory other than the ASCII-representation. However, in order to distinguish clearly between commands, control characters and data - only ASCII-coded addresses should be used. It is strongly advised to use only ASCII-coded addresses otherwise the reliability of data transfer will decrease.

 

(examples of valid address bytes:

0x30, 0x30 (=0x00);

0x39, 0x46 (=0x9F);

0x41, 0x35 (=0xA5)

 

 

PC62 with RS485 Protocol

Command - ‘RESET’

To abort a calibration cycle or to put the probe back into a known status apply the RESET command.

When a calibration is done it is possible to return the probe to normal operation with the RESET command.

 

Reset Probe (Cmnd=0xFF)