Measuring Exceeding Voltage with TB-4300B

Issue Details

Some customers are using  tests application where the standard voltage in Europe is needed  (230Vrms-240Vrms) with the TB-4300B. There have been concerns on whether that would be a problem or if they have any wiggle room, and any suggestions to work around this. 

Solution

• The max voltage input on the TB-4300B is 300 Vpk, not RMS. So with 240 Vrms applied, they are exceeding the max input voltage at ~339 Vpk.

• The attenuation ratio is 30:1, and the 4300 analog input range is ±10 V (with approximately 5% overrange capability per the user manual). As a result, a 339 V peak input would exceed the allowable input range and drive the analog input into saturation. Therefore, the module cannot accurately measure a signal of that magnitude.

• The isolation rating is 300 Vrms, so a 240 Vrms signal remains within the specified isolation limit. As a result, the isolation barrier is not expected to break down, and there should be no safety concern related to isolation.

• However, 339 Vpk (240Vrms) exceeds the 300 Vpk maximum input voltage rating. This places the terminal block and associated resistor divider outside their specified operating range. While such a condition is unlikely to cause damage to the module, operation beyond the published ratings cannot be guaranteed.

• A suggestion is to put an external resistor (rated for this voltage) in series with the 1.2 MOhm input (of the TB-4300) to divide down the signal ~10% to get within the rated range of the module.