Model 8681 Miniature RTD Surface Probe
Description
The Model 8681 ~iatie RTD Swface Probe K a 100Q, platim-type, 4-conductor, raistive tempera- detedor.
The RTD tip offe~ a flat swface tith
~d smface mea
to fadtate titicd swface tempwati me~waen~.
RTD TIP
. . . . . . . . . . . . . . . . .:.:..
:O:m
::fl~ u.09–
Fi&re 1. Model 8681 RTD probe
. . . . . . . . . . . . . ..s .. . . . .
INNER TFE TEFLON SLEEVE
@
OUTER TFE TEFLON SLEEVE
r
L
TEFLON SLEEVE
,
. . . . . .. . . . .
‘7
4-CONDUCTOR WIRE
Nets: The lead wires are 7 inches long to
allow mnnefion with the Model
2001 +CAN Scanner Cam.
7“
H
.
/
GB RW
w
100Q
a
SCHEMATIC
Tabk 1. Kit coqomts
KeiWey
Qw.
1 CA-105 ~ able md pmk
To avoid a sho& h~ad ad possible k~ent dmage, do not use thk pmdud to meavol~~ exceeding 30V RMS, Q4V pe~.
P* .0. Ddption
PA-367 Rev. A/ 4-92
Specifications
Total len~
Lead tie me
Wtie tisdation md sleeve
Mafiu voltage*:
RTD type
Notid resistance
Tip dtiensiom
Temperate range (RTD):
Tempera&e rmge (wtie):
Cment
SeU-he.&g coefficient - (°C/mW)
Respome tie h seconds T to 0.5 step
(Step = 10”C)
.Como” modeto
~D substiate.
39.37 (1.Om)
26 AWG, stimded. O.W stipped md bed ends
TWon@
42V K or AC peak
Tti-ti platim, 4-tire, ~385
100Q at O°C
O.OY x 0.08 x O.W (1.27mm x 2.03mm x 2.28mm)
-200 to +600”C
45 to +200”C
0.1tow
Water floting @ 0.~/sec...005O5
h flotig @ lM/s&...2.2
Water floting @ 0.~/sec...15l5
Air floting @: lM/sw...5.5
Model 8681 Error terms
Model 2001 RTD temperature readtigs ae based on the 4-wfie resktance measurements of platinum (resistance
temperate detectors). As the temperate ties, its r~fitance inmeasa as we~, although not in a ltiear reamer.
There me vtiom emor terns that must be added to the basic acmaq spefications of m RTD in close tolerance
~PPlicatiOns. hong fiem are the tolermce of the RTD, its se~-heating charaderistics, md themal offset voltages
mtioduced by cometions to the detedor.
RTD tolerance
Tolerance of the Model 8681 m~k or exceds the foUowtig specifications:
BS 19041984 Class A
DN 43760-1980 Class A
IEC 751:1983 Clms A
ES C1604-1981 0.2
In accordmce tith D~ EC 751, the pefisible deviations for pktim r~istmce elements (tolermce ~ade Cbss
A) me detetied by the foUotig quatiom
Petisible detition h ‘C = + (0.15 + 0.002 It I)
where It I k tie absolute tempe~awe h “C. Table 2 shows the pe~sible detiation k ohs md ‘C.
Table 2. Pmissible dmiatiorrs
Memhg
tempmtie
“c
Pefiible detition
(aa55 A)
n
“c
m
Self-heating
A additiond emor tem & due to se~-heatig of the ~D. Stice a _nt mmt be smrmd ttiugh the detice to
pmtide a voltage tit@& me~wed, the mat muse FR heatig tith the RTD, &a@g i& tempera~.
%M-heatig effe& me deatibed by the foUoting quatiom
%U-heatig emr = F x R x FK
wh~e I k the souce uent
R k the reaiatmce of the detector at a given temperate
EK k the se~-heatig coefficient h “C/mW
For _ple, the Mdel 2001 Mrdtieter somces about 0.6h WS h 4-tie, nomd speed, tith auto zero on. The
Model ml has a Seu-heatig coefitient of 0.2”C/mW h & flotig at lm/sec. With t~ probe, tie temperate
& due to W-heatig at O°Cwotid be
%H-heahg emr =Px RxEK
= (0.6ti)2 x 1~ x 0.2”C/mW
= O.oon”c
Note that whm the Mtiel 2w1 k meas~g temperate with m R~, the rwolution k O.O1OC,so this emor tem
value codd show up ~ one comt.
Thermal offsetvoltages
Themd ofiet volbg~ me generatd by temperate dfierences at the ju~on of dissti~ met&. Th& voltaga
me titioduced by the platim-t~copper comrdom that ae made when the KTD k memmed.
The the Mdel 2~1, 4-tie rffiiatmce measmaents of R~ me made h the nomd mmer, but dtig the mea-
summt pmces, themd voltagm me aceUed out tith the offset compensate ohms featie. ~ cmceUation
k arhievd by mtig WO memwma&
c The fit me~ement is the voltage amms the S~SE Q4- H md LO te~ tith ment flotig
tkough the R~ prob.
● me swond mewement is mde tith the no -nt flotig though the probe.
me voltige memmemen~ w thm wd by the Mdel 2001 to cdtiate the tempaatie. Became the R~ h= m
on/off qde, the off qde Wows th- voltagm to h measti. fro, probe heatig k ducd.
F-2 ~ows a s~ematic of the ofiet volbg~ somc~ when wtig a Model 8&l R~ prob. V, through V, repWnk tha contad voltages generatd by dkstim met&. Vm k the voltage developd amoss the probe
when uent I k flotig.
Model 8681 /
4-wire
Platinum RTD ~
+-O ;> In::
‘f
‘Rm
c
Fi&m 2. Off*t voltage sources ofR~ resistance measurmmt
RRm
V5
+
h:
I
V1
~2 I
+
I“p”t
Jack
Input Terminals
I
I
I
&nse
1 ~4.wire
HI
1
Model 2001
v~-vm=v2+vm+v5+v3
With no mat flotig, the voltage btien the Wo tetids *.
v~-vm=v2+v5+v3
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