The Oil Level Indicator (OLI) was developed in response to the need of maintenance professionals to gauge the oil level inside transformer tanks. The OLI is a clear acrylic column with 1/2″ NPT threads at each end. Red and green level marker stickers are included with the OLI to mark upper and lower limits, or to designate running oil level and idle oil level. Utilizing the drain port, operators can visually monitor the fluid level within reservoirs. Generally OLI is located on conservator for main tank and OLTC part. Digital or analog signal ouput can be supplied by different manufacturers.