The voltmeter has been calibrated prior to shipment and should provide years of service. If it is found that the voltmeter needs recalibration it is recommended that the transformer be returned to ISE for calibration. If the customer has qualified personnel and wishes to adjust the calibration the procedure below can be followed at his or her own risk. Any damages caused by improper handling or adjustment during this procedure may void the warranty on the unit.
Calibration should only be performed by qualified technicians. During the procedure there will be exposed electrical connections with dangerous voltages. This creates possible hazards to the person performing the calibrations and also can cause damage to the device if not handled carefully.
Equipment Required:
Certified Digital Voltmeter AC Volts set to appropriate range for the unit under test.
Trim Pot Insulated Adjustment Tool such as VISHAY SPECTROL - 008T000 or similar.
Note: Calibrations are made by comparison using a certified voltmeter of adequate accuracy. The percentage dial on the transformer are for reference only. Since the transformer outputs a ratio of the input source voltage the digital voltmeter and the percentage dial correlation can change due to changes with the source voltage.
1) Disconnect power from the transformer by unplugging its cord.
2) Remove the screws holding the metal cover that contains the digital voltmeter. Carefully lift the cover. Wires will limit how far the cover can be moved. Be careful to not put too much force on wire connections.
3) Situate the cover so that connections are safe and are not going to touch the metal housing of the transformer. Tape should be used for protection from exposed connections as needed.
4) Connect a certified digital voltmeter to the output.
5) Carefully connect power and turn on the unit.
6) Allow unit to warm up 20 minutes minimum.
7) Set the output of the Variable Transformer to minimum setting.
8) Compare the reading on the Unit Under Test (UUT) voltmeter with the certified voltmeter. Carefully adjust the OFFSET potentiometer on the back of the UUT voltmeter for proper displayed value. Much care must be used while making this adjustment since exposed, dangerous voltages will be present. The recommended trim pot tool or similar must be used for safety and to prevent possible damage to the transformer.
9) Set the output of the Variable Transformer to 90% of maximum setting.
10) Compare the reading on the Unit Under Test (UUT) voltmeter with the certified voltmeter. Carefully adjust the SPAN potentiometer on the back of the UUT voltmeter for proper displayed value. Much care must be used while making this adjustment since exposed, dangerous voltages will be present. The recommended trim pot tool or similar must be used for safety and to prevent possible damage to the transformer.
11) Repeat steps 7-10 as required. Also confirm proper readings at 10%, 30%, 50%, 70% & 100%.