Thermocouple Potentiometer P6

The Cropico Type P6 is a precision portable thermocouple potentiometer and calibrator designed for high-accuracy temperature measurement and instrument testing. It utilises a null-balance galvanometer system to measure or source low-voltage DC signals.

Key Features

• Voltage Range: Typically provides a range of 0–100 mV or 0–130 mV, suitable for calibrating all standard thermocouple types (K, J, T, E, R, S).
• Dual-Cell System: Employs an internal 1.5 V dry cell as a working battery and a precision standard cell (Weston type) as a voltage reference for internal standardization.
• Cold Junction Compensation (CJC): Includes an integrated precision thermometer and a manual CJC dial to compensate for ambient temperature variations at the input terminals.
• Housing: Traditionally housed in a robust leather or teak carrying case, designed for field engineers and laboratory technicians.

How It Operates

1. Standardisation (Internal Calibration)
Before use, the operator must "standardise" the instrument. This involves balancing the 1.5 V working battery against the internal precision standard cell. The galvanometer is used to find the "null" point, ensuring the potentiometer's slide-wire is energized by a precisely known current.

2. Measurement Mode (Potentiometer)
In this mode, an external thermocouple is connected to the input terminals.

• The operator adjusts the calibrated dials until the galvanometer indicates a null balance (zero current flow).
• At this point, the voltage produced by the thermocouple exactly matches the voltage set on the dials.
• The temperature is then determined by referencing the millivolt reading against standard thermocouple tables, adjusted for the ambient temperature shown on the built-in thermometer.

3. Source/Calibration Mode (Millivolt Source)
In this mode, the P6 acts as a stable voltage generator to test other instruments (such as temperature indicators or recorders).

• The operator sets the dials to a specific millivolt value corresponding to a desired temperature.
• The P6 "injects" this stable EMF into the device under test to verify its accuracy.

4. The Precision Resistor Network
The internal circuit consists of a high-stability Manganin resistor network. This network ensures that the voltage steps provided by the dials remain linear and temperature-stable during operation.

Here you find 5 models, 5 with images and 1 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from CROPICO, Croydon Precision Instruments; Croydon