What makes DataMetrics VME/PCI chassis more reliable, and keeps them on top of the VME/PCI market? Well the answer is simple; DataMetrics VME/PCI chassis are smarter than your average chassis. What makes them smarter? DataMetrics has developed a monitoring and control system that makes our VME/PCI chassis the most sophisticated, self-protecting chassis on the market. The Envirostat™ enables our VME/PCI chassis to monitor and control their internal temperatures, power supply voltages, system voltages and fan speed before damage can be done or data lost. Now lets take a look at how the Envirostat works.

What is the Envirostat?
A data acquisition system and operator interface is implemented on a circuit card that is also used to mount the VME chassis control switches. The Envirostat also includes a wide temperature range 24 Vdc power supply that provides power to the cooling fans. This power supply and the power supply for the Envirostat module are independent of the main VME system power supply.

The Envirostat automatically monitors the chassis’ operating environment to protect against damaging departures from proper operating conditions. Warnings and faults are indicated, both with indicator lamps and readable messages to alert personnel to the cause of the fault.

Additional functions available include logging of fault occurrences, provision for remote monitoring and control functions using an RS-232 link, and convenient control software revision and customization procedure.

Temperature Monitoring
This module provides to the system user temperature data from the chassis power supply, air inlet port, and fax exhaust port. The data is constantly checked for fault conditions by a microprocessor and may be monitored using the eight character alphanumeric display provided. Two additional temperatures can be monitored for applications that require that additional locations be monitored. These might include high power CPU assemblies or other on-board components.

The Envirostat computer makes use of temperature sensor data to regulate chassis temperature by adjusting fan speed. This is accomplished by controlling a digital to analog converter that determines the Envirostat fan power supply voltage. Protection against power-on is provided when the ambient temperature is outside the programmed limits.

Up to three cooling fans are intelligently monitored and controlled. The fan drives are fault monitored and should a fan stop functioning the remaining fans can be commanded to operate at higher speeds.

VME Chassis Power Supply Voltage Monitoring
The Envirostat observes the primary system DC voltages. Voltage excursions that constitute a fault condition are detected and announced using both indicator lights and the alphanumeric display. Because the Envirostat uses a high speed ten bit analog to digital converter, rapid, accurate testing is performed before declaring that a fault condition is indeed present.

As with all measured parameters, the VME chassis is deactivated under fault conditions automatically unless overruled by the operator.

Diagnostic Mode
If no faults are present the Envirostat can be set in a diagnostic mode to report system measurements to the alphanumeric display. Three switches are added to the standard control switches. These are known as F1, F2 and F3. F1 is used to scroll through the list of voltage measurements, F2 scrolls through the temperatures, and F3 will display fan status. These switches also are used to display code space checksum and select remote transmission via RS-232. The standard data rate is 19.2kb.

Circuit/Software Implementation
An 8-bit 8051 microcomputer is programmed to supervise a 1-millisecond system measurement cycle. VME system voltages are scaled with precision resistors and presented to a multiplexer for selection and buffering.

The buffered sample is presented to a 10-bit A/D converter and within a few microseconds the 8 most significant bits are stored in a memory location corresponding to the parameter. A 4.096-volt precision reference is used for the A/D converter and also buffered to excite the thermistor networks. Modern high-speed 5-volt op amps are used to provide low impedance.

After all voltages have been measured a second multiplexer is similarly accessed to measure the temperature of the fan sensors. These slowly changing parameters are sampled using sub-commutation and the data profile is accumulated over ten cycles. Some data that is typically noisy is further filtered through software averaging to provide reliable data.

After a high-speed frame is acquired it is examined for fault or warning application. A fault limit and warning limit profile is stored in table form in the microcomputer. If a limit is exceeded that parameter is immediately rechecked twice. If all measurements concur a fault is declared.

If normal operation continues the control panel is monitored for operator requests such as VME RESET, POWER DOWN, etc. These control panel switches are monitored through two 8-bit ports and debounced by multiple sampling. The display is updated through two output ports, one of which is an 8-character 5x7 dot matrix LED display. The other port drives the LED enunciators.

A third 8-bit port is used to configure the VME backplane reset control and fan activation. Four spare input lines and four spare output lines are provided (TTL level). A 2kb eeprom is present to log diagnostic information should that option be required.

A VME that can monitor and control its internal systems, adjusting them before damage can be done, is a VME for today’s high-tech military.