Technical Parameters
| Technical parameter | Parameter value |
| Brand | SONBEST |
| Noise range | 30~130dB |
| Noise accuracy | ±3% |
| Interface | RS485/TTL/DC0-3V |
| Power | DC5V 1A |
| Running temperature | -30~80℃ |
| Working humidity | 5%RH~90%RH |
Product Selection
Product DesignRS485,TTL,DC0-3VMultiple output methods, the products are divided into the following models depending on the output method.
| Product model | output method |
| SM7901B | RS485总线 |
| SM7901TTL | TTL |
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Communication Protocol
The product uses the RS485 MODBUS-RTU standard protocol format, and all operation or reply commands are in hexadecimal data. When the device leaves the factory, the default device address is 1, and the default baud rate is: for modules and non-recording instruments: 9600, 8, n, 1 (for the recorder series products, the default is: 115200, 8, n, 1).
1. Read data (Function code 0x03)
The inquiry frame (in hexadecimal). Example of sending: To query 1 piece of data of device No. 1, the host computer sends the command: 01 03 00 00 00 01 84 0A .
| Address | Function code | Starting address | Data length | Checksum |
| 01 | 03 | 00 00 | 00 01 | 84 0A |
For a correct inquiry frame, the device will respond with data: 01 03 02 02 18 B9 2E , and the response format is:
| Address | Function code | Length | Data 1 | Checksum |
| 01 | 03 | 02 | 02 18 | B9 2E |
Data description: The data in the command is in hexadecimal. Taking Data 1 as an example, 02 18 converted to decimal value is 536, the data magnification factor is 10, then the true value is 536/10 = 53.6 dB, and the others can be deduced by analogy.
2. Common Data Address Table
| Configuration Address | Register Address | Register Description | Data Type | Value Range |
| 40001 | 00 00 | noise | Read Only | 0~65535 |
| 40101 | 00 64 | Model Code | Read-only | 0~59999 |
| 40102 | 00 65 | Total Number of Measuring Points | Read-only | 1~1600 |
| 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 Query |
| 2 Active Upload | 40106 | 00 69 | Protocol Type | Read/Write |
| 1 MODBUS-RTU | Others Unused |
For example, the range is 30~130dB, the analog output is 0~3V DC0-3Vvoltage signal, noise and DC0-3Vvoltage The calculation relationship is as shown in the formula: C = (A2-A1) * (X-B1) / (B2-B1) + A1, where A2 is noise range upper limit, A1 is the lower limit of the range, B2 is DC0-3Vvoltage output range upper limit, B1 is the lower limit, X is the currently read noise value, and C is the calculated DC0-3Vvoltage value. The list of commonly used values is as follows:
| DC0-3Vvoltage(V) | noiseValue (dB) | Calculation Process |
| 0 | 30.0 | (130-30)*(0-0)÷(3-0)+30 |
| 1 | 63.3 | (130-30)*(1-0)÷(3-0)+30 |
| 2 | 96.7 | (130-30)*(2-0)÷(3-0)+30 |
| 3 | 130.0 | (130-30)*(3-0)÷(3-0)+30 |
As shown in the above formula, when measuring 1.5V, current DC0-3Vvoltage is 50dB。