Modbus
From July 15th, 2019, Modbus TCP protocol will be added to all PRECISE-LOG series of data loggers. A Modbus master/client can read one or more Input Registers and Holding Registers available in a PRECISE-LOG data logger through Modbus TCP communications.
The below specifications list all supported commands and available registers PL-TW data logger supports:
Input Registers:
An Input Register stores a 16-bit integer for a channel’s real-time reading. To read one or more 16-bit Input register data, use function code 4.
| Register |
Description |
Type |
Range |
| 0 |
CH0 Value |
Unsigned Integer |
0 - 65535 |
| 1 |
CH1 Value |
Unsigned Integer |
0 - 65535 |
| 2 |
CH2 Value |
Unsigned Integer |
0 - 65535 |
| 3 |
CH3 Value |
Unsigned Integer |
0 - 65535 |
| 4 |
CH4 Value |
Unsigned Integer |
0 - 65535 |
| 5 |
CH5 Value |
Unsigned Integer |
0 - 65535 |
| 6 |
CH6 Value |
Unsigned Integer |
0 - 65535 |
| 7 |
CH7 Value |
Unsigned Integer |
0 - 65535 |
| 8 |
CH8 Value |
Unsigned Integer |
0 - 65535 |
Example:
To read CH2, CH3 and CH4's real-time values, a Modbus master device sends in the following command:
| Data(HEX) |
Description |
Note |
| 0001 |
Transaction identifier |
Fixed 2-byte value |
| 0000 |
Protocol identifier |
Fixed 2-byte value |
| 0006 |
Length(6 bytes are followed) |
2-byte value |
| 01 |
The device address |
1-byte value, don't care |
| 04 |
Function Code (read Input Register) |
1-byte value |
| 0002 |
First register's address |
2-byte value |
| 0003 |
The number of required registers (read 3 registers 0002 to 0004) |
2-byte value |
Holding Registers:
A Holding Register stores a 16-bit integer indicating a setting for the data logger. To read one or more 16-bit Holding Register data, use function code 3.
| Register |
Description |
Type |
Range/Equation |
| 0 |
Sample Interval |
0: below 1 second
>=1: sample interval in second |
0 - 65535 seconds |
| 1 |
Device Operating Mode |
0: logging stopped
1: logger is logging data |
|
| 10 |
CH0 Type |
0:thermistor |
|
| 11 |
CH0 Enabled |
0:disabled
1:enabled |
If a channel is disabled, the reading is unknown |
| 12 |
CH0 Equation |
0: thermistor |
Range: -40 to + 70 ℃ / -40 to 158 ℉
Equation for Metrics:
O = 110 * I / 65535 - 40
Equation for Imperial:
O = 198 * I / 65535 - 40 |
| X0 |
CHX-1 Type |
0: Wide Range |
-8 to + 74 mV |
| 1: Narrow Range |
-2 to + 18 mV |
| X1 |
CHX-1 Enabled |
0: Disabled
1: Enabled |
If a channel is disabled the reading is unknown |
| X2 |
CHX-1 Equation |
0: Wide-Range Voltage |
Voltage Equation (mV)
O = 81 * I / 65535 - 8 |
| 1: Wide-Range TC E |
-171 to + 955 ℃ / -275.8 to + 1751 ℉
Temperature Equation (Metrics):
O = 1126 * I / 65535 – 171
Temperature Equation (Imperial):
O = 2026.8 * I / 65535 – 275.8 |
| 2: Wide-Range TC J |
-205 to + 1200 ℃ / -337 to + 2192 ℉
Temperature Equation (Metrics):
O = 1405 * I / 65535 – 205
Temperature Equation (Imperial):
O = 2529 * I / 65535 - 337 |
| 3: Wide-Range TC K |
-270 to + 1372 ℃ / -454 to + 2501.6 ℉
Temperature Equation (Metrics):
O = 1642 * I / 65535 -270
Temperature Equation (Imperial):
O = 2955.6 * I / 65535 – 454 |
| 4: Wide-Range TC N |
-270 to 1300 °C / -454 to 2372 ℉
Temperature Equation (Metrics):
O = 1570 * I / 65535 - 270
Temperature Equation (Imperial):
O = 2826 * I / 65535 - 454 |
| 5: Wide-Range TC T |
-270 to + 400 °C / -454 to +752 ℉
Temperature Equation (Metrics):
O = 670 * I / 65535 - 270
Temperature Equation (Imperial):
O = 1206 * I / 65535 - 454 |
| 6: Narrow-Range Voltage |
Voltage Equation (mV):
O = 20 * I / 65535 – 2 |
| 7: Narrow-Range TC E |
-35 to + 260 °C / -31 to +500 ℉
Temperature Equation (Metrics):
O = 295 * I / 65535 - 35
Temperature Equation (Imperial):
O = 531 * I / 65535 - 31 |
| 8: Narrow-Range TC J |
-40 to +330 °C / -40 to +626 ℉
Temperature Equation (Metrics):
O = 370 * I / 65535 -40
Temperature Equation (Imperial):
O = 666 * I / 65535 - 40 |
| 9: Narrow-Range TC K |
-53 to +437 °C / -63.4 to +818.6 ℉
Temperature Equation (Metrics):
O = 490 * I / 65535 - 53Temperature Equation (Imperial):
O = 882 * I / 65535 - 63.4 |
| 10: Narrow-Range TC N |
-81 to +532 °C / -113.8 to +989.6 ℉
Temperature Equation (Metrics):
O = 613 * I / 65535 - 81Temperature Equation (Imperial):
O = 1103.4 * I / 65535 - 113.8 |
| 11: Narrow-Range TC T |
-55 to +353 °C / -67 to +667.4 ℉
Temperature Equation (Metrics):
O = 408 * I / 65535 - 55
Temperature Equation (Imperial):
O = 734.4 * I / 65535 - 67 |
| 12: Narrow-Range TC B |
0 to 1820 °C / 32 to +3308 ℉
Temperature Equation (Metrics):
O = 1820 * I / 65535
Temperature Equation (Imperial):
O = 3276 * I / 65535 + 32 |
| 13: Narrow-Range TC R |
-50 to +1539 °C / -58 to 2802.2 ℉
Temperature Equation (Metrics):
O = 1589 * I / 65535 - 50
Temperature Equation (Imperial):
O = 2860.2 * I / 65535 - 58 |
| 14: Narrow-Range TC S |
-50 to +1704 °C / -58 to 3099.2 ℉
Temperature Equation (Metrics):
O = 1754 * I / 65535 - 50
Temperature Equation (Imperial):
O = 3157.2 * I / 65535 - 58 |
| 15: Linear |
O = (LRH – LRL) * I / 65535 + LRL
Where:
LRH is Linear Range high value
LRL is Linear Range low value
You can get those values from SiteView |
Where X = 2,3,4,5,6,7,8,9
O = Output, I = Input Register Value
Example:
To read CH3's equation, a Modbus master device sends in the following command:
| Data(HEX) |
Description |
Note |
| 0001 |
Transaction identifier |
Fixed 2-byte value |
| 0000 |
Protocol identifier |
Fixed 2-byte value |
| 0006 |
Length(6 bytes are followed) |
2-byte value |
| 01 |
The device address |
1-byte value, don't care |
| 03 |
Function Code (read Holding Register) |
1-byte value |
| 002A |
First register's address (42 is 2A in HEX) |
2-byte value |
| 0001 |
The number of required registers (read 1 registers 002A) |
2-byte value |
Note:
- Modbus feature was added to firmware version 2.05 or above.To upgrade a data logger's firmware please refer to this link: How can I upgrade logger firmware?
- The age of an Input Register data is based the data logger's sample interval.If the logger has stopped logging or the logger's sampling interval is slower than five seconds, a request of Input Register data will initiate the sampling process and the new data will be available upon the next request.
