DATA SHEET T-78
TYPE 78B
RIGID PROBE WITH HEX FITTING
Features: 1/4" diameter sheath available in 316
stainless steel or Inconel welded to threaded hex
fitting for connection head assembly. Operating
range to 2100°F defined by the sheath material,
thermocouple type and the temperature at the
welded fitting.		  

TYPE 78D
SPRING-LOADED PROBE
Features: 1/4" diameter sheath, available in 316 stainless steel or Inconel. Proprietary spring-load design insures positive thermal contact and prevents probe rotation during vibration. Operating range to 2100°F defined by the sheath material, thermocouple type and the temperature at the spring-load fitting.
Thermowell must be specified for this probe. See Data Sheet T-WELLS.
Performance Specifications
Features
_ FM and CSA listed
_ ANSI types J, T, K, E; Traceable to NIST
_ Special Limits of Error
_ Single or dual junctions
_ Stainless steel fittings
_ Inconel or stainless steel sheaths
_ TIG welded construction
_ Strong and flexible stranded 20 AWG leads,
    fiberglass insulated and jacketed cable
_ 500°F Lead exit rating
_ Stainless steel or aluminum lag unions
_ Cast aluminum heads with up to 8 terminal posts

Thermowells & Connnection Heads
See Data Sheet T-WELLS for representative
approved configurations.
Response Time of Model 78B
(in water flowing at 3 ft/sec)
Ungrounded: < 5 seconds
Grounded: < 2.5 seconds
Approvals
RdF assemblies are approved for
Class I Div. 1 Groups B, C, D;
Class II Div. 1 Groups E, F, G;
and Class III Hazardous locations.
Measuring Junctions
The thermocouple wires are welded directly to the sheath end closure and are completely protected. Recommended for fast responding 78B direct immersion probes. Isolated instrumentation required.
The thermocouple junction is electrically insulated from the external sheath with compacted magnesium oxide powder. Recommended in all applications to minimize instrumentation ground loops.
 

THERMOCOUPLE MATERIAL RANGE AND LIMITS OF ERROR*
ANSI Type
Callibration		 Positive Negative
(red)		 Color Code
(positive conductor)		 Temperature Range
°F (°C)		 Standard
(whichever is greater)		 Special
(whichever is greater)
J Iron
(Magnetic)		 Constantan White 32 to 1330 (720) ±4°F or ±0.75% ±2°F or ±0.4%
K Chromel Alumel
(Magnetic)		 Yellow –320 to 32 ± 4°F or ±2% -
32 to 2100 (1150) ±4°F or ±0.75% ±2°F or ±0.4%
T Copper
(Copper Color)		 Constantan Blue –320 to 32 ±1.8°F or ±1.5% -
32 to 700 (370) ±1/8°F or ±0.75% ±.90°F or ±0.4%
E Chromel Constantan
(Silver Color)		 Purple –320 to 32 ±3°F or ±1% -
32 to 1510 (820) ±3°F or ±0.5% ±1.8°F or ±0.4%
 

*Limits of error are new material interchangeablity only.
Ordering Specifications
78B
78D		 Explosion Proof Rigid Thermocouple with MGO Insulated Sheath and Connection Head
Explosion Proof Spring-Loaded Thermocouple with MGO Insulated Sheath, Connection Head and Thermowell
 
  SHEATH DIAMETER (Series 78 available with 1/4" Dia. only)
     4
 
     SHEATH MATERIAL
S
I
 316 Stainless Steel
Inconel 600
 
     ANSI TYPE THERMOCOUPLE – (Special Limits of Error)
J
K
T
E		 Iron/Constantan
Chromel/Alumel
Copper/Constantan
Chromel/Constantan
 
  NUMBER OF JUNCTIONS
S
D		 Single
Double
 
  LENGTH IN INCHES –
  PROBE LENGTH:  78B - “L” in inches – See drawing (1/2" min.)
78D - “A” in inches - See drawing
STEM LENGTH: (2" min., x + A = 24" max.)
 
   TYPE OF JUNCTION
G
U
Grounded
Ungrounded
 
   CONNECTION HEAD
G
H
Small Cast Aluminum (250°F max. rating)
Small Cast Aluminum (500°F max. rating)
 
 LAG HARDWARE (78D only, see drawings)
 – stainless steel or noted
A
 Hex Nipple is 3/4" long standard.
Specify as “A”
BX (Straight nipple), specify X=3", 6", 9",
or 12" max.
EX (Aluminum union/nipple extension),
specify X=min. 3" + 1" increments to 12" max.
FX Same as EX (stainless steel union)
 
LEAD LENGTH in Inches (4" STD.)
78B
_
_
–
4
_
_
–
S
_
_
–
J
_
_
–
S
_
_
–
6
_
_
–
U
_
_
–
H
_
_
  –  
4
_
_
–

Typical write-up for 78B
78D
_
_
–
4
_
_
–
S
_
_
–
K
_
_
–
S
_
_
–
8
_
_
–
U
_
_
–
G
_
_
–
B3
_
_
–
4
_
_
– Typical write-up for 78D
_
Dimensional Drawings 1/2 NPT Lag Hardware
RdF Corporation • 23 Elm Ave., Hudson, NH 03051-0490  
800.445.8367 • 603.882.5195 • fax 603.882.6925 • www.rdfcorp.com