T7 Networked Absolute Inclinometer

Note: The T7 can drive 100 ft. of cable. Some PCs have limited drive on the RS232 bus which will limit the maximum cable length to less than 100 ft.

Notes:

1) Uses RS485 two-wire network

2) Uses "fail-safe" drivers so bias resistors are not required

3) In most applications, the RS485 network does not need termination at 9600 bps with less than 1000 feet of cable. If termination is used, the RS485 network should be terminated with a 120-150 ohm resistor between BUS+ and BUS- at the source and at the last T7-1-485/T7-1-MOD4 on the network. US Digital terminating CAN cables (CA-CM-PS-CFTR) may be used at the last T7 on the bus to terminate it.

For a given network size, a minimum T7-1-485/T7-1-MOD4 power supply voltage is needed to ensure that the last T7 on the network is powered by at least 5.5V. The minimum power supply voltage can be calculated based on the number of networked T7s, the cable resistance/configuration, and the current consumption of each T7 as a function of voltage. The following tables show the recommended minimum power supply voltage as a function of cable length and number of T7s for several common network wiring schemes. The tables assume that US Digital T7 cables with a resistance of 3.3 ohms per hundred feet (#22 AWG) for the two power lines are used. USD T7 cables have a twisted pair for the data wires and can be used for both RS485 and RS232 versions. The following data is for room temperature (22C) operation.

Recommended minimum power supply voltage for T7s equally spaced on a total cable length, L. Stub length from T-adapter to a T7 is 6 feet. N is the number of T7's in the network.

Recommended minimum power supply voltage for T7s spaced 9 feet apart after an initial leader cable length, L. Stub length from T-adapter to a T7 is 6 feet.

The RS232 and RS485 versions of the T7 are available with the Modbus RTU protocol. Modbus Function Codes 3 (Read Holding Register) and 6 (Write Single Register) are supported. User defined Function Code 110 is used for some operations such as setting serial port parameters and the device address. If non-US Digital Modbus devices are connected to the same bus, it is recommended that only Function Codes 3 and 6 be used for non-USD devices.

• Up to ±5° off-axis operation is possible with 2σ (95%) confidence on the maximum angular error

• Measurements taken at 25°C
• Damping time is a user programmable parameter

Axis Orientation:

Note: T7 shown with factory default configuration.

The T7 uses a FIR (Finite Impulse Response) digital filter to provide electronic damping of the angle readings. The digital filter's impulse response has a triangular weighting that decays linearly to zero. The damping time is user programmable from 2 milliseconds to 5000 milliseconds.  Since the sensor bandwidth is 8 Hz, damping times below 125 milliseconds do not provide any faster response. Increasing the damping time will average more samples together to form the reported angle. This will reduce noise in the output but increase the response time.

An inclinometer network assembled with the RS232 or RS485 version of the T7 is shown below.

US Digital sells all the cables and connectors needed to wire a T7 network. The T7 uses the same connector for all interface versions.

Regardless of the interface option, a host PC, PLC, or microcontroller communicates with a network of T7s by sending/receiving simple serial port commands over the RS232 or RS485 bus. 

T7-1-232, T7-1-485 Addressing

Each T7 on the network must be assigned a unique address from 1 to 100 or 127 (decimal). Address assignment is optional for the RS232 version. All T7s are shipped with a default address of 127. Address 126 is a special broadcast address - all T7s will listen and respond to commands sent to this address. To assign an address to a T7 unit, connect one T7 to a PC using a USB to RS232/RS485 adapter. The address can be set using the included PC-based "T7 Demo" software. Alternately, a host computer can send the "Set Address" serial port command to the T7. This procedure only needs to be done once for each T7 since the address is stored in non-volatile flash memory.

T7-1-MOD2, T7-1-MOD4 Addressing

Each T7 on the network must be assigned a unique address from 1 to 100 (decimal). All T7s are shipped with a default address of 127.  Address 0 is the Modbus broadcast address. To assign an address to a T7 unit, connect one T7 to a PC using a USB to RS232/RS485 adapter. The address can be set using the included PC-based "T7 Demo" software. Alternately, a host computer can send a special  "Set Address" command to the T7. This procedure only needs to be done once for each T7 since the address is stored in non-volatile flash memory.

All T7 units ship from US Digital with a default configuration.  Configuration parameters are stored in non-volatile flash memory and can be easily changed by the user. The specifications are shown below.  However, in larger quantities, units can be preconfigured with any of the available settings noted in the T7 Communication User Guide or T7 Modbus Communication User Guide.  Please contact customer service.

Default Configuration:

• Address = 127
• Single-axis version uses Axis 2
• Angle output range set to +/-180 (-179.99 to 179.99) deg.
• Counting Direction set to "forward"
• Angle Offset set to 0
• Damping time = 1000 milliseconds
• USD protocol versions use 115200 bps, 8 data bits, no parity, 1 stop bit
• Modbus protocol versions use 9600 bps, 8 data bits, even parity, 1 stop bit