BARTINGTON INSTRUMENTS
Page 59 of 82 OM0408/49
19.1. Internal Power Distribution
Filtered mains supply is rectified and smoothed, and supplied to transistors which control the
voltage supplied to the furnace. Furnace current is monitored by a meter on the front panel. A
DC regulated supply is provided for the internal circuitry. A DC supply is fed to the digital panel
meter and associated circuitry, and a precision reference voltage is provided for temperature
offset and control purposes.
19.2. Temperature Control
Temperature is controlled in two ways.
1. Temperature is pre-set on the 10-turn dial, thermostatically maintained.
2. Temperature is programmed to increase or decrease with time in a linear fashion at a rate
pre-selected on the 10-turn dial.
In both cases, analogue temperature information from the MS2WF is compared to an internally
generated reference (proportional), and the resulting error information (integral) is used to
maintain the correct temperature.
Temperature rate of change (differential) information is measured to minimise over- and
undershoot which could occur when selecting a new temperature. Maximum current is
limited to 4A (cold furnace) by a safe operating area monitor. The platinum furnace's high
positive temperature coefficient of resistance will limit this current to 3A maximum at elevated
temperatures.
19.3. RS-232 Buffer
With a computer, MS2 meter and MS2WF connected to the appropriate connectors, the RS-232
serial data between the computer, the MS2 meter and the MS2WF digital panel meter are routed
through the MS2WFP.
The computer transmits characters 'Z' and 'M' which are recognised by the MS2 meter, causing
a zero and measure operation respectively. The measurement value is transmitted back to the
computer at the end of the measurement period. The computer also transmits data strings
which are recognised by the temperature meter and cause it to set the appropriate thermocouple
linearization, or take a reading, as required. The meter responds by transmitting an ASCII
character string.
The temperature meter has an RS485 interface and a 232/485 converter is used at the
temperature meter terminals. The signals from the MS2 meter and temperature meter are
output through the same RS-232 connector to the computer.
