Wahl 2500MX User manual

W -683 Rev G
Revised 02/03/23
HEA T - PROBER
®
POR T ABLE THERMOCOUPLE
THERMOMETERS
INSTRUCTION MANUAL
LCD Models LED Models
2500MX
1370MX
2500M
2500MVX 1370MVX 1370M
3200MX 1770MX 3200M
3200MVX 1770MVX 1770M
TCMR-K
TCMR- KX
TCMRK-VX

RECEIVING INSPECTION
Check your new W ahl Portable Thermocouple Heat-Prober Thermometer upon
Receiving to assure that:
1. It has not been physically damaged in transit.
2. All parts are included.
Then, plug in the probe at top and turn it on to see that it reads room temperature.
If a fault is determined, take the following steps:
1. Notify the W ahl factor y of the difficulty . Give model number and description.
W ahl will authorize return, and notify our service department to receive the
unit.
2. Return the instrument in its shipping container to the factor y, freight pre-
paid. Repairs will be made under warranty or at regular service cost.
3. Prepare a “Repair Information Form” as shown in Section 12.0 and return
with the instrument. This is ver y important. W e need the information to
diagnose the problem. If there is no information returned with the unit, it
will slow up the repair process.
ii

T ABLE OF CONTENTS Page
RECEIVING INSPECTION . . . . . . . . . . . . . . . . . . . . . . .ii
1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2.0 OPERA TION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
2.1 Meter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.2 Peak Hold (MAXI-TEMP) . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.3 Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
2.3.1 Recharging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
2.3.2 Low Batter y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
2.3.3 Continuous Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.0 PROBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
3.1 Open Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
3.2 T emperature Sensors in use . . . . . . . . . . . . . . . . . . . . . . .11
4.0 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . .14
5.0 CALIBRA TION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
5.1 V oltage Regulator Adjustment . . . . . . . . . . . . . . . . . . . . . 17
5.2 Low Batter y Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . .17
5.3 Calibration Using W ahl Calibrator . . . . . . . . . . . . . . . . . . .18
5.3.1 Zero Adjustment Using W ahl Calibrator . . . . . . . . . . . . . . 18
5.3.2 Span Adjustment Using W ahl Calibrator . . . . . . . . . . . . . .18
5.4 Calibration With a Millivolt Sour ce . . . . . . . . . . . . . . . . . .18
5.4.1 Zero Adjustment with Millivolt Sour ce . . . . . . . . . . . . . . .18
5.4.2 Span Adjustment with Millivolt Sour ce . . . . . . . . . . . . . . .20
5.5 Thermal Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
5.6 Calibration with Thermocouple Simulator . . . . . . . . . . . . .22
5.7 T A-70 Thermocouple Calibrator . . . . . . . . . . . . . . . . . . . .22
6.0 THEORY OF OPERA TION . . . . . . . . . . . . . . . . . . . . . .27
6.1 V oltage Regulation Cir cuitr y . . . . . . . . . . . . . . . . . . . . . . .29
6.2 V oltage Reference Cir cuitr y . . . . . . . . . . . . . . . . . . . . . . .29
6.3 Front End Cir cuitr y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.4 Cold Junction Compensation . . . . . . . . . . . . . . . . . . . . . .30
6.5 Dual Slope A/D Converter . . . . . . . . . . . . . . . . . . . . . . . . .30
6.6 8048 Microprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.7 Waveforms and T iming Diagrams . . . . . . . . . . . . . . . . . . .31
6.8 Low Batter y Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
iii

7.0 BASIC TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . .33
8.0 MAINTENANCE AND REPAIR . . . . . . . . . . . . . . . . . . .36
8.1 LED and LCD Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . .36
9.0 APPENDIX IPTS-86 AND IPTS-90 . . . . . . . . . . . . . . . .42
10.0 ADDITIONAL PROBES AND ACCESSORIES . . . . . . . . .51
11.0
RETURN FOR REPAIR/CALIBRATION . . . . . . . . . . . . . .52
FIGURES Page
Figure 1-1 Microprocessor Based Thermocouple Digital Therm. . . . . .2
Figure 2-1 Digital Heat Prober Major Features . . . . . . . . . . . . . . . . . . .4
Figure 2-2 Rechargeable Batter y Pack Compartment . . . . . . . . . . . . . .6
Figure 3-1 Heat Prober Thermocouple T ypes, Model Numbers . . . . . .8
Figure 3-2 Standard W ahl Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Figure 3-3 Extension Probe Handle . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Figure 3-4 Molten Metal Dip Stick . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Figure 5-1 W ahl Calibrator T ypes . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Figure 5-2 Heat Prober With W ahl Calibrator . . . . . . . . . . . . . . . . . . .24
Figure 5-3 LED Adjustment Points . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Figure 5-4 LCD Adjustment Points . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Figure 6-1 Program Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Figure 6-2 Microprocessor Control Functions . . . . . . . . . . . . . . . . . . .32
Figure 7-1 Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Figure 8-1 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Figure 8-2 LED Component Layout . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Figure 8-3 LCD Component Layout . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Figure 11-1 Additional Probes and Accessories . . . . . . . . . . . . . . . . . .50
iv

1
1.0 INTRODUCTION
W ahl Thermocouple Digital Heat-Prober Thermometers are precision Instruments for
measuring temperature, with special attention to ruggedness of design. They provide
the certainty of a digital display over the wide range of temperatures available with
thermocouples from -100°F to 3200°F (-70°C to 1770°C). The Heat-Prober is a com-
plete instrument with a battery power supply and recharger. It is inter changeable with
30 different thermocouple probe configurations designed for rapid sensing of temper-
ature in ever y application.
The Heat-Prober series accommodates two thermocouple types.
1. T ype K (Nickel Chromel-Nickel-Alumel) for general purpose use from
-100 to 2500°F (-70 to 1370°C).
2. T ype S (Platinum-Platinum/10% Rhodium), for high temperature use from
77 to 3200°F (25 to 1770°C).
All of the Heat-Prober instruments use common circuitr y. Microprocessors hold the
thermocouple tables in memor y and provide digital processing and control of the
information.
The instrument contains the unique W ahl MAXI-TEMP® digital peak cir cuit, which
gives the user the option to hold the highest temperature sensed. The peak-hold
cir cuit is achieved by the microprocessor scanning the probe input temperature to
determine the highest temperature reached. This peak is locked digitally and there is
no drift.
The meter has a convenient standard miniature temperature compensated connector
socket for easy use and inter changeability with similar thermocouple type probes.
A large portion of the cir cuit is designed with low power C-MOS components. In addi-
tion, the LED displays are multiplexed. The result is a design which provides a low
power drain and allows longer operation time on rechargeable batteries. Continuous
operation is also possible with the recharger attached. In both cases, the instrument is
powered from the batteries. Both LED and LCD models have a large character size for
good readability.

2
Figure 1.1. Microprocessor Based Thermocouple Digital Thermometer
(LED display, left; LCD display, right)

3
All Heat-Prober instruments are extensively tested in environments from
-20°F to 140°F for specification compliance and reliability determination. In addition,
durability testing includes impact, vibration, battery life and running life tests. Mean
time between failure is based on using preburned-in C-MOS electronic components
and is rated at 16,000 hours.
The 9-volt LCD models with 50-hour standard alkaline batteries, replaceable from the
back cover, are designated models 1370MVX, 1770MVX, 2500MVX and 3200MVX.
They have the same specifications as the rechargeable LCD models.
2.0 OPERA TION (See Figure 2-1)
Insert probe into socket at the top of the instrument. T u rn on the switch at the left. The
switch is 3-position; the lower detent is marked “N” for normal temperature monitor-
ing, the middle detent is “OFF’ and the upper detent is marked “P” for use with W ahl
Maxi-Temp peak hold cir cuit. This tracks the temperature and holds the highest attained
reading. If “L”, or “←”, appears or if there is no reading, this indicates the battery is
discharged. For models MVX, change the 9-volt battery. Recharge the unit by inserting
the recharger in a 110 V AC, 50-60 Hz wall outlet and plug in the recharger jack to the
instrument socket on the left. (T urn the instrument switch OFF during recharging, to
maximize recharge rate. Charge for 10-12 hours)*. T u rn on instrument again.
Make measurements with sensor probe as required. T u rn
off switch when measure-
ments are complete to preser ve battery life.
*Special Note on Care of Rechargeable Batteries, See Paragraph 2.3

4
Figure 2-1. Digital Heat-Prober Major Features

5
2.1 Meter Operation
The Heat-Prober instrument has an accurate measuring range as stated on the front
label. When the temperature is below zero, a minus sign will automatically show on
digital display. Absence of a sign indicates positive temperature.
2.2 Peak Hold (MAXI-TEMP)
MAXI-TEMP peak hold is a standard feature on all models. With the switch in “P” or
peak hold position, it will sense positive increases in temperature and hold the highest
reading. This is convenient in making measurements where attention to the probe or
to the area being measured occupies the operator. The peak reading is held digitally by
the microprocessor and will not drift. T o remove the peak reading, switch to “OFF”, or
to “N”.
2.3 Batteries (Figures 2-2)
The Heat-Prober is powered with five size AA rechargeable nickel-cadmium batteries,
1.25 volts each. The total capacity is 450 milliampere hours at 6.0 volts. The LED
display demands the largest power drain. Depending on the number of digits being
displayed, the batteries can power the instrument for a minimum of 5 hours or for as
long as 6 hours (with LCD display, the life is approximately 12 hours).
An alternate replaceable 9-volt alkaline transistor radio-type battery powers meters
with “V” designations in their part number. The instrument has a voltage regulation
which will accept and control the power from the 9-volt battery. These instruments do
not allow for recharging. Under special cir cumstances LED models 2500M, 1370M
and 1770M may be operated with disposable 9-volt alkaline batteries with an approxi-
mate 3 hour battery Iifespan. (Figure 2.2)
SPECIAL NOTE: Rechargeable batteries should be kept at full charge. On the shelf,
they will gradually discharge, losing about 10% charge per week. If the battery fails to
respond to recharge, provisions have been made for ease of replacement. Open the
back cover and disconnect from the instrument by means of the Molex connector.
Replace with W ahl P/N 11681 (See Figure 2-2).

6
Figure 2-2. Replaceable 9V Batter y Pack Compartment (above)
Rechargeable Batter y Pack Compartment (below)

7
2.3.1 Recharging
T o recharge the batteries, use the recharger supplied. Plug in directly to a 120-volt,
60-cycle wall plug and insert the jack into the socket on the left side of the Heat-
Prober. (For overseas 220-volt lines, use a Franzus converter adapter with the recharg-
er supplied or request a 220-volt recharger).
2.3.2 Low Batter y
Ni-Cad batteries have a stable voltage throughout their charge life. Near the end of the
power cycle the voltage will drop abruptly. This voltage is sensed by the meter.
Low-battery indication is registered on the display by “L” on LED models and “LO
BA TT”, or “←”, on LCD models. This indicates that you have approximately two minutes
to complete your measurement. After that, the falling battery voltage may cause erro-
neous readings. Continued use of the meter will result in total loss of display. The
recharger should be put on immediately after the low battery light comes on. Recharge
time is 10 to 12 hours, but a partial charge can be obtained in 1 hour or less.
2.3.3 Continuous Operation
The Heat-Prober can be continuously operated by using a battery recharger to restore
or recharge the batteries as they are depleted. The instrument operates from the bat-
teries only. The recharger will charge the batteries with the switch “OFF”, or make-up
battery power when the instrument is operating. The recharger supplied with the
instrument will enable continuous operation. It the battery pack is in an extremely low
charge condition, it may take two to three minutes before the display will function.
NOTE: The instrument cannot rectify AC current. A DC charger with open cir cuit volt-
age of 9 volts and approximately 120 milliamperes will maintain the battery charge.
This occurs when the switch is on and the instrument is operating. Do not connect a
voltage sour ce to the batteries unless its current is limited to 120 milliamperes.

8
3.0 PROBES
One of the key features of the W ahl Thermocouple Heat-Prober is a standard miniature
thermocouple connector used in the meter. Thermocouple connections are color
coded by type. Use probes with the same color male plug as the female. Each Heat-
Prober is designed for use with a specific thermocouple T ype K or S. A thermocouple
of the same type with a standard male thermocouple connector will fit the meter. No
adapters are needed. The thermocouple is compensated where the cold junction is
made and cold junction compensation occurs automatically.
Each meter face indicates the thermocouple type, the temperature range of use, and
the calibration in °F or °C, as shown in Figure 3-1.
THERMOCOUPLE TYPE RANGE MODEL-NO.
T ype K (Y ellow) -100°F to 2500°F
(-70°C to 1370°C)
2500M
2500MX
2500MVX
1370M
1370MX
1370MVX
T ype S (Green) 77°F to 3200°F
(25°C to 1770°C)
3200M
3200MX
3200MVX
1770M
1770MX
1770MVX
Figure 3-1. Heat-Prober Thermocouple T ypes and Models

9
W ahl offers three classes of probes:
1. Portable probes with their own handles, cables and miniature connectors as
shown (Figure 3-2). These include unique replaceable tip sur face probes,
straight and right angle, air sensors, immersion sensors, and miniature tip
sensors.
2. Extension handle with replacement tip probes (Figure 3-3).
3. A DIP-STICK
®
probe for molten metals, offered with a rugged meter carrier
and one-shot T ype K or S platinum rhodium replaceable tips (Figure 3-4).
Portable Probes
T o use the hand-held probes (Models TC801 and TC821), you simply plug in the probe
to the meter.
CAUTION: Thermocouple tip probes should not be used on high voltage equipment
because the element is not electrically isolated. If such use is needed consult the fac-
tor y for a special design.
W ahl specializes in sur face temperature measurement probes. Models TC808, 809,
and 810 are exposed element sur face probes for fast sur face temperature measure-
ments. Because these elements are exposed, there may be loss due to wear or break-
age. Therefore, TC809 was designed with replaceable “Z” tips which plug into the end
of the handle. T wo types, straight or right angle, are available by designating TC821
replaceable tips.
Extension Handle: For heavy-duty, everyday production and where an extension is
needed to properly position the probe, the TC829 extension handle with armored cable
is recommended (Figure 3-3). A series of replaceable Up probes is available for attach-
ment to the end of the extension handle.
Dipstick for Molten Metals: The meter and probe are mounted on an extension tube,
as shown in Figure 3-4. The meter is removable from the stick. This special meter and
probe combination comes in two ranges:

10
Figure 3-2. Standard W ahl Probes
Figure 3-3. Extension Probe Handle

11
Thermocouple Type K (Model TC830): For 2500°F (1370°C) with expendable type K
tips. Useful for molten non-ferrous metals. The meter is removable from the handle
and therefore can be used elsewhere with any of the other W ahl probes.
Thermocouple Type S (Model TC840): For 3200°F (1770°C) in ver y high temperature
iron and steel melts. The quartz encased probe junction can usually be used more than
once. When broken or consumed, the tip is simply pulled out of the Dipstick tip and a
new one inserted. The tip is made with tight contact. Grasp the expendable tip by the
ceramic shoulder and push it hard into the holder.
CAUTION: The quartz tip breaks easily . Do not drop it or push on the quartz tip.
Three types of tips are available: Exposed ceramic tip for small dips of up to1-3/4 inch
immersion, and two types of tips with aluminum splash shield and 12-inch cardboard
shaft for penetration through slag up to 12 inch immersion.
3.1 Open Probe
If the thermocouple sensor loses continuity , or if no sensor is connected to the meter,
the display will show “-OL-”, indicating out-of-limit reading.
3.2 T emperature Sensors in Use
An understanding of heat transfer is needed for accurate field use of temperature
sensors. The sensor measures its own temperature. Therefore, to measure a body
temperature, it requires good contact with that body. In the case of liquids or gases,
good immersion and mixing are necessar y.
A portable probe temperature sensor must have the following characteristics:
(a) A low thermal mass (product of its specific heat and weight).
(b) A large area for sur face contact to permit heat transfer between the object
being measured and the probe sensor.
(c) A minimum of heat conduction away from the sensor which will reduce the
temperature below that of the object being measured and create an inaccuracy.

12
Figure 3-4. Molten Metal Dipstick

13
Wahl’s sur face probes are designed with the above conditions as criteria. They also
include an insulating handle for your safety and convenience. Each probe is assembled
with a plastic handle made of high-quality Delrin which:
a) Thermally isolates the hand from the probe, preventing hand heat from
reaching the sensor, and sensor heat, in the case of high temperature meas-
urement, from burning the hand.
b) Electrically isolates the hand from the metal probes and therefore, potentially,
from a voltage on the sur face to be measured.
T o obtain best time responses and accuracy of sur face measurements, two conditions
are necessar y:
a) Good sur face contact with all of the probe sur face. Ensure this by holding it
squarely on the sur face. The TC868 and TC869 sur face probes are specially
designed with a spring loaded tip to provide compliance with the sur face.
b) Good heat conductance to the measuring probe. A rough sur face can be
overcome by applying a thin layer of heat-conducting silicone paste between
the measuring point and the probe tip. The paste shortens indicating time
up to 50%.
In liquids, move the immersion probe around and mix to get good contact. In air, put
the probe in the vicinity of a stream to get good velocity, or move the probe back and
forth to induce velocity across the tip.
For bolt-on or stick-on probe/sensors, it is recommended that an insulating layer of
cement be placed over the unit after installation to prevent heat loss to the surroundings.

14
4.0 SPECIFICATIONS
T emperature Measurement Range
Model T/C Type Range Display
T/C 2500M K -100 to 2500° LED
T/C 2500MX K -100 to 2500° LCD
T/C 2500MVX K -100 to 2500° LCD
T/C 1370M K -70 to 1370° LED
T/C 1370MX K -70 to 1370° LCD
T/C 1370MVX K -70 to 1370° LCD
T/C 3200M S 77 to 3200° LED
T/C 3200MX S 77 to 3200° LCD
T/C 3200MVX S 77 to 3200° LCD
T/C 1770M S 25 to 1770° LED
T/C 1770MX S 25 to 1770° LCD
T/C 1770MVX S 25 to 1770° LCD

15
Display:
Resolution:
Repeatability:
Accuracy:
0.3” high LED, 0.4. High LCD
Automatic Polarity Indication
Open Probe: Indicated by “OL”
Low Batter y: Indicated By “L” on LED
“LOW BA T”, or “←”, Annunciator on
LCD Update Rate: 2.5/Sec.
±1
±1°F , ±1 digit
±.2% Reading ±1 digit
Thermocouple Probe: Standard miniature thermocouple connector
Connections: A) Y e llow T ype K
B) Green T ype S
Environmental
T emperature Range: -20 to 140°F (-28 to 60°C)
T emperature Less than 0.05° degree/degree
Coefficient: over ambient range of -0° to 120°F (-20°to 50°C).
Batteries: Five pack size AA rechargeable nickel cadmium batteries
@ 6.25 V nominal. Batteries are removable from the rear
cover plate and disconnected as a unit via a connector.
Replaceable 9 volt transistor battery in “V” models.
Batter y Life: MVX Models: 50 hours
M and MV Models: 8 hours per charge
Low Batter y Indication: Low Batter y displays “L” on LED display
“LOW BA T” on LCD display.

16
Recharger: 7.5V @ 120mA from 11Ovac line.
Line Operation: Continuously operable from recharger through
internal batteries.
Effects of High AC No damage or display effect at 120 vac.No damage at
V oltage on Probe: 500 vac
Size and W eight: 3” wide x 6” long x 11/2” high. 12 oz.
(7.5cm x 15cm x 3.7 cm; 340 gm.)
Mode of Operation: A) Normal
B) Peak-Hold: holds last peak reading. Digitally implemented.
C)Off.
Linearization: Microcomputer corrected over the entire range.
Based on IPT -S68 cur ves to 0.5°F (.05°F for T ype T).
Peak Hold: Microcomputer -calculated switch to “P” to activate
(holds and displays highest reading).
Probe Connection: Standard miniature thermocouple connector
(female) compensated.
Noise Rejection: Greater than 40DB at 60Hz increasing at 20DB per decade.
Spurious noise is attenuated by internal 16Hz filter .
W a rm-up: Instantaneous.
Cold Junction Internal at female thermocouple
Compensation: connector, automatic.