What functions does a transformer oil tester provide in field diagnostics?

Field testers provide rapid screening of oil condition to support maintenance and troubleshooting. The most common function is BDV testing to estimate dielectric strength. Many portable devices also measure moisture in ppm, temperature, and sometimes conductivity or dielectric loss indicators. These tools help verify oil handling quality after filtering or filling, assess suspected moisture ingress, and decide whether a unit can remain in service until full laboratory results arrive. Field testing does not replace lab DGA, but it speeds decisions and reduces downtime during outages.