What is the Isolator Calibration Meter ?
The QAT isolator control systems control automatically by modulating the speed signal to both supply and exhaust fans. This is switchable from PWM (pulse width modulated) to 0-10 VDC analogue. For nearly all isolators, 1-10 VDC analogue controlled fans are used. This is mainly because PWM is generally reserved for use with the smaller gas blower type fans as in the PCI and AMU. For certain test and diagnostic work it can be useful to send a manual control signal to the fans. As this is not provided for in the control system, this piece of equipment does just that.
The meter is attached to the circuit board using the peripherally arranged push on terminals, and it replaces the automatic 0-10 VDC signal with a manually generated one. Two potentiometers and two digital volt meters allow the test engineer to see the fan speed signal being sent along with the voltage. Toggle switches allow switching between either auto or manual control and displaying either control voltage
Applications
The Isolator Calibration Meter is designed for use only with QAT isolator control systems using 0-10 VDC analogue controlled fans. It can also be used to the same effect on ACE units
How does it work?
The Isolator Calibration Meter plugs into the circuit board fan connection terminals between the board and the fan. It takes the constant 24 VDC signal available from the terminal and passes this through a 23 turn potentiometer in the meter. This modulated signal is then passed to the fan as its DC analogue control signal in place of the automatically generated signal available from the terminal middle contact.
The knob on the calibration meter now manually controls the fan speed. A digital voltmeter on the meter also shows the signal voltage level for reference. This is repeated on the meter for a second channel such that both supply and control fans can be controlled and monitored simultaneously
Advantages
The Calibration Meter allows the test engineer to take over fan control and investigate the voltage or fan duties. The automatic control function of the circuit board can also be tested by sending a low manual signal and monitoring the auto signal on the digital display. This is useful in fault finding or checking that the system has enough capacity during development
