In-Situ · Water quality sensor
Level TROLL 400 / 500 / 700 / 700H (Modbus PLC interface) Modbus register map
Default configuration
- Protocol
- RS485
- Port
- 502
- Unit ID
- 1
- Addressing
- 0-based
- Byte order
- Big endian
- Word order
- High word first
- Baud rate
- 19200
- Parity
- Even
- Data bits
- 8
- Stop bits
- 1
This device has an RS-485 interface. Reach it through a Modbus RTU-to-TCP gateway, configured with the factory serial settings above.
Register map
| Address | Count | Name | Type | Unit | Scale | Access |
|---|---|---|---|---|---|---|
| 37 | 2 | Pressure Measured value of parameter 2; 32-bit float, big-endian. Factory default unit is PSI (unit ID 17); the unit is set through the unit register at address 40. | Float32 | PSI | 1 | R |
| 39 | 1 | Pressure data quality 0 = no errors or warnings, 3 = error reading the parameter. | UInt16 | - | 1 | R |
| 40 | 1 | Pressure units Unit ID for the pressure parameter: 17 = PSI (factory default), 19 = kPa, 20 = bar, 21 = mbar, 22 = mmHg, 23 = inHg, 24 = cmH2O, 25 = inH2O. | UInt16 | - | 1 | RW |
| 41 | 1 | Pressure parameter ID Parameter ID = 2. | UInt16 | - | 1 | R |
| 42 | 2 | Pressure offline sentinel value Value returned on error or when the parameter is unavailable; factory default 0.0. | Float32 | PSI | 1 | RW |
| 45 | 2 | Temperature Measured value of parameter 1; 32-bit float, big-endian. Factory default unit is °C (unit ID 1); the unit is set through the register at address 48. | Float32 | °C | 1 | R |
| 47 | 1 | Temperature data quality 0 = no errors or warnings, 3 = error reading the parameter. | UInt16 | - | 1 | R |
| 48 | 1 | Temperature units Unit ID for the temperature parameter: 1 = °C (factory default), 2 = °F. | UInt16 | - | 1 | RW |
| 49 | 1 | Temperature parameter ID Parameter ID = 1. | UInt16 | - | 1 | R |
| 50 | 2 | Temperature offline sentinel value Value returned on error or when the parameter is unavailable; factory default 0.0. | Float32 | °C | 1 | RW |
| 53 | 2 | Depth / Level Measured value of parameter 3 (depth) or 4/5 (level, depth to water / surface elevation, enabled in VuSitu), which share this starting register. Factory default unit is feet (unit ID 38); the unit is set through the register at address 56. | Float32 | ft | 1 | R |
| 55 | 1 | Depth / Level data quality 0 = no errors or warnings, 3 = error reading the parameter. | UInt16 | - | 1 | R |
| 56 | 1 | Depth / Level units Unit ID for the depth/level parameter: 38 = feet (factory default), 33 = mm, 34 = cm, 35 = m, 37 = inches. | UInt16 | - | 1 | RW |
| 57 | 1 | Depth / Level parameter ID Parameter ID: 3 = depth, 4 = level (depth to water), 5 = level (surface elevation). | UInt16 | - | 1 | R |
| 58 | 2 | Depth / Level offline sentinel value Value returned on error or when the parameter is unavailable; factory default 0.0. | Float32 | ft | 1 | RW |
| 9000 | 1 | Device ID 30 = Level TROLL 400, 1 = Level TROLL 500, 2 = Level TROLL 700 / 700H, 3 = Baro TROLL. | UInt16 | - | 1 | R |
| 9001 | 2 | Device serial number 32-bit serial number. | UInt32 | - | 1 | R |
| 9006 | 1 | Firmware version For example 100 = firmware 1.00. | UInt16 | - | 1 | R |
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Related guides
Notes
Source: In-Situ 'Level TROLL 400, 500, 700, and 700H Operator's Manual', part number 0052212, document revision 2024-23-01 ((c) In-Situ 2023), vendor-hosted PDF at the URL above (opened 7 Nov 2026): section 'Modbus PLC Interface' (page 47 onwards) and Appendices A (parameter numbers and locations) and B (unit IDs). Factory serial settings from the Modbus PLC Interface chapter: Modbus RTU, 1 start bit, 19200 baud, 8 data bits, even parity, 1 stop bit, default device address 1. Addressing: the manual prints a 'Holding Register Number' next to a 'Holding Register Address' that is exactly one lower (device ID 9001 / 9000, temperature 0046 / 0045, pressure 0038 / 0037, depth 0054 / 0053), states that some PLCs need 40000 added to the register number, and its worked example adds the block offsets to the register number before subtracting one - the numbers are decimal (pressure block 38-44, temperature 46-52, depth 54-60), and the addresses are stored unchanged as zero-based wire addresses (37, 45, 53). Every parameter block is 7 registers long: value (2 registers, big-endian float), data quality (1), unit ID (1), parameter ID (1), offline sentinel value (2). All rows are holding registers and the manual states that each register is a holding register. Default units come from Appendix A (temperature 1 = °C, pressure 17 = PSI, depth/level 38 = feet) and are writable through the unit-ID registers. Operating notes from the same chapter: the instrument must be woken with a carriage return (0x0D) or any Modbus command, one second must pass before the next command, and the default end-of-session timeout is 5 seconds (longer after a VuSitu session), so readings must be requested before it expires. Not claimed: the Baro TROLL variant's parameter set and the SDI-12 side of the device.