Substitute for Siemens Grenzwertmelder Type P49-007

The indicator in the photo looks like a 1950's analog temperature indicator. The wiring diagram shows that it has a couple of alarm relays or on/off control relays. The red pointers are the setpoint indicators for alarm relays (some kind of mechanical adjustment drives them back and forth across the scale)

The Messwert terminals 1 (+) and unmarked terminal 2 might are likely connections for the

thermocouple sensor. The symbol on terminals 1 & 2, a circle is a diameter line through the center, is not a thermocouple or an RTD symbol in the United States; might it be so in Germany (it happens to be the medieval symbol for salt, sodium chloride)?

It's hard to tell how linear the scale is, thermocouple scales are visibly non-linear, RTD scales are quite linear. But there's a greater likelihood that the sensor is a thermocouple because thermocouples are polarized (+), (-). RTD's being passive resistors, are not.

The American made temperature indicatorsof that era typically had a notation on the indicating scale specifying the type of thermocouple that the meter was designed for, but it typically was not a letter designation, it was an abbreviation like Cr/Al ior C/A (Chromel/Alumel) for type K. The photo is tooout of focus to make a determination, but it appears that there might be notation on the lower left portion of the indicating scale. Maybe there's a clue there as to the type of thermocouple. Many indicators of that range, 0-150°C, were iron/constantan, Type J thermocouples.

The other way to get a clue for the thermocouple is to examine sensor's wiring insulation to see what its color coding is. Given the German heritage, you might want to refer to a German thermocouple color code table.

If it were a type J thermocouple, I'd replace the sensor; the iron leg is most likely oxidized over its 60+ years of work.

When the word "Limit" is used along with temperature (as in limit monitor), it frequently indicates the necessity for a latching alarm with manual reset, to force human intervention to reset the alarm before the process is re-initiated. If that's the case for the shaft temperature that this device monitors, be sure to get a replacment indicator whose alarm relays can be setup to latch and which has a convenient reset button. Not all indicator alarms will latch.