Hampshire Controls Corporation
20 Mar. 2021
MPS Operating Manual
Page 5
Sensor Probe
The probes supplied with your system may vary depending on custom options. Commonly used
probes are:
Pt100 (100 ohm platinum) RTD
Type-T thermocouple
Type-K thermocouple
HX-71 relative humidity transmitter (voltage output)
Heated cryogenic Pt100 RTD (for LN2 level sensing)
Switch (mechanical or magnetic reed)
The most common probe option is the Pt100 RTD, a highly accurate resistive temperature
device. The sensor element is enclosed in a 4 inch long and 3/16 inch diameter stainless steel
sheath. The standard lead length is 10 feet of FEP jacketed 3-conductor wire. Custom lead
lengths may be specified when ordering. The probe sheath may be placed in water or other mild
aqueous solutions from -100°C to 100°C.
The probes will be pre-wired to terminal-block plugs which mate with the pluggable terminal-
block sockets on the back of the MPS. Each connection will be marked with identifying
information about the probe or relay connection and any other pertinent electrical information.
Please take care when making connections, as the terminal-block sockets are all physically
identical but may be VERY different electrically. For instance, with an MPS-2HT (humidity and
temperature) the MPS supplies 15VDC to the humidity transmitter. If you were to plug the
Pt100 RTD probe into the socket for the humidity transmitter you may permanently damage the
RTD element or the MPS electronics due to Electrical Over-Stress (EOS).
NOTE:
Avoid submerging the probe in solvents or harsh chemicals. Use protective thermowells
when monitoring such materials.
NOTE:
The warranty does NOT cover damage to probes or electronics that is caused by
exceeding temperature limitations, or damage to probes caused by using them in solvents or
other unsuitable environments.
NOTE:
If the displayed temperature shows a consistent high (> 100°C) or low (< -100°C)
value, most likely, the probe has failed. The unit should be returned for probe replacement and
recalibration.
Probe Installation
The probe may be used in air, water, or simulated product (usu. glycol or glass beads).
If installing the sensor in a cabinet or enclosure (particularly freezers), make sure to use good
techniques to prevent room moisture from getting into the cabinet. Whenever possible, install the
probe through an existing access port provided by the cabinet manufacturer, then reseal the port.
Alternatively, the probe can be run under, over, or through the door-sealing gasket. Often a door
gasket will have a joint at one or more corners. Open that joint slightly by carefully making a slit
with a razor blade. Insert the probe wire and then reseal the joint with flexible silicone sealing
compound. Inside the cabinet, run the probe wire so that it will not become snagged during
loading, unloading or cleaning procedures.
