Technical Parameters
| Technical parameter | Parameter value |
| Brand | SONBEST |
| Temperature measuring range | -30℃~80℃ |
| Temperature measuring accuracy | ±0.5℃ @25℃ |
| Humidity measuring range | 0~100%RH |
| Humidity accuracy | ±3%RH @25℃ |
| Interface | RS485/4-20mA/DC0-5V/DC0-10V |
| Power | DC12~24V 1A |
| Running temperature | -30~85℃ |
| Working humidity | 5%RH~90%RH |
Product Selection
Product DesignRS485,4-20mA,DC0-5V,DC0-10VMultiple output methods, the products are divided into the following models depending on the output method.
| Product model | output method |
| SM3720B | RS485总线 |
| SM3720M | 4-20mA |
| SM3720V5 | DC0-5V |
| SM3720V10 | DC0-10V |
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Communication Protocol
The product uses RS485 MODBUS-RTU standard protocol format, all operation or reply commands are hexadecimal data. The default device address is 1 when the device leaves the factory, and the module or NON-Recorder default baud rate is 9600,8,n,1 ,but data recorder default baud rate is 115200 .
1. Read data (function code 0x03)
Inquiry frame (hexadecimal), sending example: query 1 data of 1# device, the upper computer sends the command: 01 03 00 00 00 02 C4 0B .
| Address | Function Code | Start Address | Data Length | Check Code |
| 01 | 03 | 00 00 | 00 02 | C4 0B |
For the correct query frame, the device will respond with data: 01 03 04 00 7A 00 00 DB EA , response format:
| Address | Function Code | Length | Data 1 | Data 2 | Check Code |
| 01 | 03 | 04 | 00 79 | 00 7A | DB EA |
Data description: The data in the command is hexadecimal, take data 1 as an example, 00 79 is converted to decimal value as 121, assuming the data magnification is 100, then the real value is 121/100=1.21, Others and so on.
2. Common data address table
| Configuration Address | Register Address | Register Description | Data Type | Value Range |
| 40001 | 00 00 | temperature | Read Only | 0~65535 |
| 40002 | 00 01 | humidity | Read Only | 0~65535 |
| 40101 | 00 64 | Model Code | Read/Write | 0~65535 |
| 40102 | 00 65 | total number of measuring points | read/write | 1~20 |
| 40103 | 00 66 | device address | read/write | 1~249 |
| 40104 | 00 67 | baud rate | read/write | 0~6 |
| 40105 | 00 68 | communication mode | read/write | 1~4 |
| 40106 | 00 69 | protocol type | read/write | 1~10 |
1. temperature and current computing relationship
For example, the range is -30~80℃, the analog output is 4~20mA current signal, temperature and current The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is temperature range upper limit, A1 is the lower limit of the range, B2 is current output range upper limit, B1 is the lower limit, X is the currently read temperature value, and C is the calculated current value. The list of commonly used values is as follows:
| current(mA) | temperatureValue (℃) | Calculation Process |
| 4 | -30 | (80-(-30))*(4-4)÷(20-4)+-30 |
| 5 | -23.125 | (80-(-30))*(5-4)÷(20-4)+-30 |
| 6 | -16.25 | (80-(-30))*(6-4)÷(20-4)+-30 |
| 7 | -9.375 | (80-(-30))*(7-4)÷(20-4)+-30 |
| 8 | -2.5 | (80-(-30))*(8-4)÷(20-4)+-30 |
| 9 | 4.375 | (80-(-30))*(9-4)÷(20-4)+-30 |
| 10 | 11.25 | (80-(-30))*(10-4)÷(20-4)+-30 |
| 11 | 18.125 | (80-(-30))*(11-4)÷(20-4)+-30 |
| 12 | 25 | (80-(-30))*(12-4)÷(20-4)+-30 |
| 13 | 31.875 | (80-(-30))*(13-4)÷(20-4)+-30 |
| 14 | 38.75 | (80-(-30))*(14-4)÷(20-4)+-30 |
| 15 | 45.625 | (80-(-30))*(15-4)÷(20-4)+-30 |
| 16 | 52.5 | (80-(-30))*(16-4)÷(20-4)+-30 |
| 17 | 59.375 | (80-(-30))*(17-4)÷(20-4)+-30 |
| 18 | 66.25 | (80-(-30))*(18-4)÷(20-4)+-30 |
| 19 | 73.125 | (80-(-30))*(19-4)÷(20-4)+-30 |
| 20 | 80 | (80-(-30))*(20-4)÷(20-4)+-30 |
As shown in the above formula, when measuring 8mA, current current is 31.5℃。
2. humidity and current computing relationship
For example, the range is 0~100%RH, the analog output is 4~20mA current signal, humidity and current The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is humidity range upper limit, A1 is the lower limit of the range, B2 is current output range upper limit, B1 is the lower limit, X is the currently read humidity value, and C is the calculated current value. The list of commonly used values is as follows:
| current(mA) | humidityValue (%RH) | Calculation Process |
| 4 | 0.0 | (100-0)*(4-4)÷(20-4)+0 |
| 5 | 6.3 | (100-0)*(5-4)÷(20-4)+0 |
| 6 | 12.5 | (100-0)*(6-4)÷(20-4)+0 |
| 7 | 18.8 | (100-0)*(7-4)÷(20-4)+0 |
| 8 | 25.0 | (100-0)*(8-4)÷(20-4)+0 |
| 9 | 31.3 | (100-0)*(9-4)÷(20-4)+0 |
| 10 | 37.5 | (100-0)*(10-4)÷(20-4)+0 |
| 11 | 43.8 | (100-0)*(11-4)÷(20-4)+0 |
| 12 | 50.0 | (100-0)*(12-4)÷(20-4)+0 |
| 13 | 56.3 | (100-0)*(13-4)÷(20-4)+0 |
| 14 | 62.5 | (100-0)*(14-4)÷(20-4)+0 |
| 15 | 68.8 | (100-0)*(15-4)÷(20-4)+0 |
| 16 | 75.0 | (100-0)*(16-4)÷(20-4)+0 |
| 17 | 81.3 | (100-0)*(17-4)÷(20-4)+0 |
| 18 | 87.5 | (100-0)*(18-4)÷(20-4)+0 |
| 19 | 93.8 | (100-0)*(19-4)÷(20-4)+0 |
| 20 | 100.0 | (100-0)*(20-4)÷(20-4)+0 |
As shown in the above formula, when measuring 8mA, current current is 29%RH。
1. temperature and DC0-5Vvoltage computing relationship
For example, the range is -30~80℃, the analog output is 0~5V DC0-5Vvoltage signal, temperature and DC0-5Vvoltage The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is temperature range upper limit, A1 is the lower limit of the range, B2 is DC0-5Vvoltage output range upper limit, B1 is the lower limit, X is the currently read temperature value, and C is the calculated DC0-5Vvoltage value. The list of commonly used values is as follows:
| DC0-5Vvoltage(V) | temperatureValue (℃) | Calculation Process |
| 0 | -30 | (80-(-30))*(0-0)÷(5-0)+-30 |
| 1 | -8 | (80-(-30))*(1-0)÷(5-0)+-30 |
| 2 | 14 | (80-(-30))*(2-0)÷(5-0)+-30 |
| 3 | 36 | (80-(-30))*(3-0)÷(5-0)+-30 |
| 4 | 58 | (80-(-30))*(4-0)÷(5-0)+-30 |
| 5 | 80 | (80-(-30))*(5-0)÷(5-0)+-30 |
As shown in the above formula, when measuring 2.5V, current DC0-5Vvoltage is 55℃。
2. humidity and DC0-5Vvoltage computing relationship
For example, the range is 0~100%RH, the analog output is 0~5V DC0-5Vvoltage signal, humidity and DC0-5Vvoltage The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is humidity range upper limit, A1 is the lower limit of the range, B2 is DC0-5Vvoltage output range upper limit, B1 is the lower limit, X is the currently read humidity value, and C is the calculated DC0-5Vvoltage value. The list of commonly used values is as follows:
| DC0-5Vvoltage(V) | humidityValue (%RH) | Calculation Process |
| 0 | 0.0 | (100-0)*(0-0)÷(5-0)+0 |
| 1 | 20.0 | (100-0)*(1-0)÷(5-0)+0 |
| 2 | 40.0 | (100-0)*(2-0)÷(5-0)+0 |
| 3 | 60.0 | (100-0)*(3-0)÷(5-0)+0 |
| 4 | 80.0 | (100-0)*(4-0)÷(5-0)+0 |
| 5 | 100.0 | (100-0)*(5-0)÷(5-0)+0 |
As shown in the above formula, when measuring 2.5V, current DC0-5Vvoltage is 50%RH。
1. temperature and DC0-10Vvoltage computing relationship
For example, the range is -30~80℃, the analog output is 0~10V DC0-10Vvoltage signal, temperature and DC0-10Vvoltage The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is temperature range upper limit, A1 is the lower limit of the range, B2 is DC0-10Vvoltage output range upper limit, B1 is the lower limit, X is the currently read temperature value, and C is the calculated DC0-10Vvoltage value. The list of commonly used values is as follows:
| DC0-10Vvoltage(V) | temperatureValue (℃) | Calculation Process |
| 0 | -30 | (80-(-30))*(0-0)÷(10-0)+-30 |
| 1 | -19 | (80-(-30))*(1-0)÷(10-0)+-30 |
| 2 | -8 | (80-(-30))*(2-0)÷(10-0)+-30 |
| 3 | 3 | (80-(-30))*(3-0)÷(10-0)+-30 |
| 4 | 14 | (80-(-30))*(4-0)÷(10-0)+-30 |
| 5 | 25 | (80-(-30))*(5-0)÷(10-0)+-30 |
| 6 | 36 | (80-(-30))*(6-0)÷(10-0)+-30 |
| 7 | 47 | (80-(-30))*(7-0)÷(10-0)+-30 |
| 8 | 58 | (80-(-30))*(8-0)÷(10-0)+-30 |
| 9 | 69 | (80-(-30))*(9-0)÷(10-0)+-30 |
| 10 | 80 | (80-(-30))*(10-0)÷(10-0)+-30 |
As shown in the above formula, when measuring 5V, current DC0-10Vvoltage is 55℃。
2. humidity and DC0-10Vvoltage computing relationship
For example, the range is 0~100%RH, the analog output is 0~10V DC0-10Vvoltage signal, humidity and DC0-10Vvoltage The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is humidity range upper limit, A1 is the lower limit of the range, B2 is DC0-10Vvoltage output range upper limit, B1 is the lower limit, X is the currently read humidity value, and C is the calculated DC0-10Vvoltage value. The list of commonly used values is as follows:
| DC0-10Vvoltage(V) | humidityValue (%RH) | Calculation Process |
| 0 | 0.0 | (100-0)*(0-0)÷(10-0)+0 |
| 1 | 10.0 | (100-0)*(1-0)÷(10-0)+0 |
| 2 | 20.0 | (100-0)*(2-0)÷(10-0)+0 |
| 3 | 30.0 | (100-0)*(3-0)÷(10-0)+0 |
| 4 | 40.0 | (100-0)*(4-0)÷(10-0)+0 |
| 5 | 50.0 | (100-0)*(5-0)÷(10-0)+0 |
| 6 | 60.0 | (100-0)*(6-0)÷(10-0)+0 |
| 7 | 70.0 | (100-0)*(7-0)÷(10-0)+0 |
| 8 | 80.0 | (100-0)*(8-0)÷(10-0)+0 |
| 9 | 90.0 | (100-0)*(9-0)÷(10-0)+0 |
| 10 | 100.0 | (100-0)*(10-0)÷(10-0)+0 |
As shown in the above formula, when measuring 5V, current DC0-10Vvoltage is 50%RH。
