X-band Solid State Transmitter Monitor User's Guide (TN-008)

This article describes the transmitter monitor board developed at CSU-CHILL. This board is designed for use in the Solid-state X-band project (WiBEX). The board monitors the operating conditions of the solid-state transmitter, and reports these to a higher-level controller. It can also shut down the transmitter in the event of a fault. The board is fully programmable via a Modbus/RTU interface.

Introduction

The transmitter monitor board is a critical component in the WiBEX radar design. Its primary task is to monitor the operating conditions of the solid-state transmitter. Secondary functions include a split power supply (+/- 5V) for the X-band microwave switches used in the front end of the WiBEX radar, a Peltier cooler driver for the X-band LNAs and a microwave switch driver.

Block Diagram

The figure below shows a block diagram of the board. The primary controller on the board is an Atmel ATMega164P microcontroller. This controller implements the main logic of the board, along with the Modbus/RTU slave logic. Various peripherals available on the microcontroller are used to interface to the analog electronics on the board.

Block Diagram

Modbus Registers

The interface to the synthesizer is through Modbus/RTU. The Modbus communications model is a single master controlling various slave devices. Each slave is addressable, and has different registers which may be read or written. This design implements read-only registers (referred to as Input Registers in the Modbus specifications) and read-write registers (Holding Registers). There are no coils or status bits available.

Input Registers

The available input registers are shown in the table below:

Register Number	Name	Description
1000	ALARM	Indicates the cause of any alarms indicated by the Modbus ALM signal. Reading the register clears the alarm condition and deasserts the Modbus ALM signal.
1001	STATUS	Indicates the operating status of the transmitter.
1002	TEMP_AMP1	Amplifier 1 temperature, in degrees C multiplied by 100.
1003	TEMP_AMP2	Amplifier 2 temperature, in degrees C multiplied by 100.
1004	FAN1_RPM	Power Amplifier cooling fan 1-4 speed, in revolutions per minute.
1005	FAN2_RPM
1006	FAN3_RPM
1007	FAN4_RPM
1008	V_AMP1	Amplifier 1 voltage, in millivolts.
1009	I_AMP1	Amplifier 1 current, in milliamperes multiplied by 10.
1010	V_AMP1	Amplifier 2 voltage, in millivolts.
1011	I_AMP1	Amplifier 2 current, in milliamperes multiplied by 10.
1012	TEMP_HOT	Peltier cooler hot-side (heatsink) temperature, in degrees centigrade multiplied by 100.
1013	TEMP_COLD	Peltier cooler cold-side (LNA) temperature, in degrees centigrade multiplied by 100.
1014	PFAN_RPM	Peltier cooler heatsink fan speed, in revolutions per minute.
1015	RP_COUNT	Reverse power pulses per second.

Input Register Map

Alarm Register

This register contains bit values that may be used to determine the cause of an alarm/fault. The bits are described below.

Bit	Name	Description
7	Peltier Overtemp	A Peltier Overtemperature event is declared when the Peltier cooler hot-side temperature (TEMP_HOT) exceeds the limit programmed in PELTIER_TEMP_HIGH.
6	Fan Failure	A Fan Failure event is declared when more than two power amplifier blowers fails. A fan failure is defined as the fan rotation speed falling below 1000 rpm.
5	Reverse Power	A Reverse Power event is declared when the reverse power detectors detect more than the number of reverse power events specified in RP_COUNT_LIMIT per second.
4	Power Amplifier Overtemp	A Power Amplifier overtemperature event occurs when either power amplifier base plate temperature exceeds PA_TEMP_HIGH.
3	Reserved
2	Reserved
1	Overcurrent Fault	An overcurrent fault occurs when either PA draws more than PA_CURRENT_HIGH amperes.
0	Under/over Voltage Fault	An overvoltage fault occurs if the PA supply voltage falls outside the range bounded by PA_VOLT_LOW and PA_VOLT_HIGH

ALARM register (address 1000)

Any fault will result in the appropriate bit being set in the ALARM register, the Modbus ALM signal being asserted, and the power amplifier power supply being shut off. Reading the alarm register clears the fault if the alarm condition no longer exists. For example, if an overtemperature event caused bit 4 to be set, but the amplifier temperature falls within the allowed window after the alarm event, reading the ALARM register will clear the fault. If the amplifier temperature is still too high, however, the fault does not get cleared.

Holding Registers

The available holding registers are shown in the table below:

Register Number	Name	Description
1000	DISP_MODE	Mode of the alphanumeric display.
1001	PA_CONTROL	Power amplifier power control.
1002	FAN_MODE	Power amplifier cooling fan mode.
1003	FAN_TGTSPEED	Target speed of the power amplifier cooling fans when in manual mode.
1004	FAN_P_FACTOR	Proportional gain for the fan speed control loop, when in automatic mode.
1005	FAN_I_FACTOR	Integral gain for the fan speed control loop, when in automatic mode.
1006	FAN_D_FACTOR	Differential gain for the fan speed control loop, when in automatic mode.
1007	RP_COUNT_LIMIT	Number of reverse power pulses per second needed to trigger an alarm.
1008	PELTIER_TEMP_SETPOINT	Temperature that the Peliter cooler tries to attain, when in closed loop (automatic) mode.
1009	PELTIER_P_FACTOR	Proportional gain for the Peltier cooler control loop, when in automatic mode.
1010	PELTIER_I_FACTOR	Integral gain for the Peltier cooler control loop, when in automatic mode.
1011	PELTIER_D_FACTOR	Differential gain for the Peltier cooler control loop, when in automatic mode.
1012	PA_VOLT_LOW	Lower limit of the acceptable power supply input voltage range.
1013	PA_VOLT_HIGH	Higher limit of the acceptable power supply input voltage range.
1014	PA_CURRENT_HIGH	Upper limit of the current that may be drawn at the power amplifier contacts.
1015	PA_TEMP_HIGH	Maximum power amplifier temperature.
1016	PELTIER_TEMP_HIGH	Maximum Peltier hot-side temperature.
1017	FAN_SPEED_LOW	Minimum rotation speed before a fan failure is declared.

Holding Register Map

Display Mode

The display mode register permits the mode of the onboard alphanumeric display to be changed. Supported display modes are shown below:

Mode	Description
0	PA 1 Voltage
1	PA 1 Current
3	PA 2 Voltage
4	PA 2 Current
5	Peltier Cooler cold side temperature
6	Peltier Cooler hot side temperature
7	Amplifier 1 temperature
8	Amplifier 2 temperature
9	Fan 1 speed
10	Fan 2 speed
11	Fan 3 speed
12	Fan 4 speed
13	Peltier cooler fan speed

Display Modes

It is not recommended to reprogram the display mode using Modbus, since the display is meant for local interaction with the board.

Fan Mode

The fan mode register selects the operating mode of the power amplifier cooling fans.

Number	Mode	Description
0	Manual	The fan target speed specified in FAN_TGTSPEED is used to control the fans.
1	Automatic	The fan target speed is automatically determined to maintain the PA temperature specified in PA_TEMP_HIGH.

Fan Modes

Fan Control Loop parameters

A PID controller is used to determine the fan speed in the automatic fan mode. The FAN_P_FACTOR, FAN_I_FACTOR and FAN_D_FACTOR are used to set the PID parameters. The parameters are internally divided by 128. There are no units assigned.

Peltier Temperature Control Loop parameters

A PID controller is used to determine the drive current to the Peltier cooler. The PELTIER_P_FACTOR, PELTIER_I_FACTOR and PELTIER_D_FACTOR are used to set the PID parameters. The parameters are internally divided by 128. There are no units assigned.