Yes the probe has two metal tip. This is where the pulse will jump between them and measure the conductivity of the fluid which in turn measures the salinity.
This is an old post but I wanted to provide some updated information. I am looking to use this exact TDS probe and I was able to determine from bench testing that the white leads are for the integral 10k-ohm thermistor and the colored leads (red in my case) are for the actual EC (TDS) measurement.
I have tried to determine the K value on the conductivity probes and based on my measurements using a pair of calipers, I am getting 7.56. I'm not 100% certain on whether the probe space is clear space or centerline spacing. These probes generally come in 0.1, 1 or 10, so I suspect it is really a K value of 10. If the K value is that high, then the sensor will not be very useful for my goal (or even the purpose it is commonly used for on RODI systems). Not 100% sure on this. As the OP stated, the data sheet is useless and HM has never responded to my requests for information. It is very clear they only want their probes used on their products....overpriced junk.
I ordered the Atlas Scientific RTD and Conductivity converters and will verify these settings.
My project is to consolidate 6 of these TDS meters from the HM Digital TRM-1's onto a single Arduino and couple this with a new LCD and RS232 shield. The LCD will allow display of each meter and select meters for calibration. The RS232 shield will be for ModBus communication with a PLC I am also building.
I will have a separate post on my project once it is underway. In the meantime, just thought I would share what I found since this was one of the posts I crossed as part of my search.