Fieldpiece SRH2 User Manual

Standalone
Diagnostic
Psychrometer
Model: SRH2

OPERATOR’S MANUAL

Description

The SRH2 is a complete digital psychrometer
and a very valuable HVAC diagnostic tool. As a psy­chrometer, it measures wet bulb (WB), dry bulb
(DB), percent relative humidity (RH%), and dew
point (DP). As a diagnostic tool, it helps the HVAC
technician easily diagnose problems with air flow
across the evaporator. It can also calculate the tar­get superheat of a fixed restrictor air conditioning
system.

Use the NORM mode (normal psychrometer) to
display wet bulb (WB), dry bulb (DB), percent rela­tive humidity (RH%), or dew point (DP).

Use TSH (Target Superheat) to help set the
proper refrigerant charge for a fixed restrictor sys­tem. Use the Fieldpiece SSX34, ASX14, or ASH3 to
easily measure Actual Superheat without the need
of additional charts.

Use TEET (Target Evaporator Exit Temperature)
to ensure proper evaporator airflow.

How it Works

The SRH2 has three sensors. One for RH% and
two for temperature. Depending on where you place
these sensors and how you set up the SRH2, the
meter will display the measurements and the results
of calculations from these inputs. DB Temperature
and RH% are measured directly. WB, DP, TSH, and
TEET are calculated and displayed. WB may be
displayed directly when using the ATWB1 wet sock
thermocouple and choosing the T/C sensor.

Inside the 'cage' on the top of the meter is a ther­mistor, right next to the RH% sensor. It's used to
measure ambient air (DB). In addition to the ther­mistor, a thermocouple can be plugged into the top
of the meter. Use a thermocouple for getting tem­peratures (including wet bulb) in hard to reach
places, such as in front or in back of the evaporator
coil.

To use the SRH2, you must tell it what test you
want it to perform. Select the parameter you want to
measure, and choose which temperature sensor to
use, either the thermocouple (T/C) or the 'caged'
thermistor (NTC). Take your measurements. Read
the results, both the directly measured readings and
the calculated results.

Thermocouple Calibration

Adjust the thermocouple measurements to match
the measurements from the built in negative tem­perature coefficient (NTC) thermistor (in the 'cage'
on the top of the meter). Here's how:

1. Plug the thermocouple into the SRH2 and put its
sensor inside the 'cage' so it's measuring the
same ambient air as the thermistor.

2. Press TSH/TEET/NORM until NORM is dis­played.

3. Press RH/DP/WB/DB until DB is displayed.

4. Press SENSOR to compare NTC and T/C read­ings. Adjust T/C Cal pot on front of meter until
readings are the same. Make sure you have
waited long enough for the sensors to stabilize.
The thermocouple (T/C) will react much faster
than the thermistor (NTC).

Battery check function:

The SRH2 allows the user to check the battery
charge at any time during use, simpily by hold­ing down the BACKLIGHT button for over one
second.
The approximate percentage of battery charge
will be displayed on the main display for two
seconds before returning to its reading prior to
preforming the battery check.

Step by Step Operation

Select °C or °F

Start with the instrument turned OFF. Press and
hold for °C or SENSOR for °F, and simulta­neously press the ON/OFF button.

Normal Psychrometer (NORM)

1. Select NORM by pressing TSH/TEET/NORM
until NORM is displayed in the lower left hand
corner of the LCD.

2. Press SENSOR to select temperature sensor:
T/C for thermocouple, NTC for sensors in the
'cage'.

3. For T/C, the display will show the temperature.

4. For NTC, press RH/DP/WB/DB until the desired
icon (RH, DP, etc.) is displayed. Then read the
display.

Target Superheat (TSH)

1. Select TSH by pressing TSH/TEET/NORM until
TSH is displayed in the lower left hand corner of
the LCD. Note: blinking numbers mean you are
seeing real-time measurements. Non-blinking
numbers mean the reading has been 'locked in'.
Press ENTER to unlock and take a new read­ing.

2.The more accurate method:

a. Wet the ATWB1. Clip it to the front of the

evaporator coil. Plug it into the top of the
SRH2. Make sure the display shows ID
and WB. If not, press RH/DP/WB/DB.

Press SENSOR until T/C is displayed.
Once the reading is stable, press

ENTER.
b. Unplug the ATWB1 and plug in the ATA1.
c. Clip the ATA1 thermocouple to the side of

the condenser. Press RH/DP/WB/DB until

OD and DB are displayed. Press SENSOR

until T/C is displayed. Once reading is sta-

ble, press ENTER. Note: for DB, you can

put the 'caged' sensors where air is entering

the condenser and select NTC if that is eas-

ier.

The easy way: While the numbers are blinking,
press SENSOR until NTC is displayed. Press
RH/DP/WB/DB until WB or DB is displayed.
When WB is displayed, place the 'caged' sen­sors in front of the indoor return and press
ENTER once reading is stable. When DB is dis­played, put the 'caged' sensors in front of the
condenser and press ENTER when the reading
is stable.

3. Press OUTPUT to display Target Superheat.

4. Compare Target Superheat to Actual Superheat.

5. Adjust refrigerant levels accordingly for a fixed
restrictor system. If Actual Superheat is higher
than Target Superheat, add refrigerant. If Actual
Superheat is lower than Target Superheat,
recover refrigerant.

Target Evaporator Exit Temperature (TEET)

1. Select TEET by pressing TSH/TEET/NORM
until TEET is displayed in the lower left hand
corner of the LCD. Note: blinking numbers
mean you are seeing real time measurements.
Non-blinking numbers mean the reading has
been 'locked in'. If numbers are not blinking
press ENTER to unlock and take a new reading.

2. Wet the ATWB1 wet sock thermocouple and clip
both thermocouples (ATWB1 and ATA1) in front
of the evaporator, (see figure 1 on next page).

3. Plug the ATWB1 into the top of the SRH2. Note:
If “OL” is displayed, then the measurements are
out of range. Retake the temperature measure­ments and ensure the temperature inputs are
correct.

4. Press RH/DP/WB/DB until WB is displayed.
Press SENSOR until T/C is displayed. When
reading is stable, press ENTER.

5. Unplug the ATWB1 and plug in the ATA1.

6. Press RH/DP/WB/DB until DB is displayed.
Press SENSOR until T/C is displayed. When
reading is stable, press ENTER.

7. Press OUTPUT and read Target Evaporator Exit
Temperature. Note: If “OL” is displayed, then
the measurements are out of range. Retake the
temperature measurements and ensure the
temperature inputs are correct.

8. Compare Target Evaporator Exit Temperature to
Actual Evaporator Exit Temperature. The Actual
Evaporator Exit Temperature is the measured
temperature of the air after it has passed
through the evaporator.

9. Adjust airflow accordingly. An Actual Evap. Exit
Temp. below the Target Evap. Exit Temp. indi­cates low airflow. Increasing airflow can be
accomplished by eliminating restrictions in the
duct system, increasing blower speed, cleaning
filters or opening registers. An Actual Evap. Exit
Temp. above the Target Evap. Exit Temp. usual­ly indicates low capacity. Occasionally airflow is
higher than expected. Look for causes of low
capacity such as refrigerant mischarge
or a dirty condenser coil. If the airflow is high,
correct it by lowering the fan speed.
Note: If “OL” is displayed, then the measure­ments are out of range. Retake the temperature
measurements and ensure the temperature
inputs are correct.

IMPORTANT:

Because everything within the system is inter­dependent, one adjustment can affect other
parts of the system. For example, increasing air­flow increases the superheat, which may require
adding refrigerant. After any modifications, allow
15 minutes to stabilize and then retest. For the
best results take measurements right after each
other.

T2

T2

FF

/O

T/C

Diagnostic
Psychrometer

°C °F

BATTERY
CHECK

T2

RH/DP/WB/DB

AUTO-OFF

MAX/MIN/H

ENTER

ON/OFF

T2ONT2

TSH/TEET/NORM

Calculates
Target SH
and Target
Evap Exit

T/C

Temperature

Cal

SRH2

NTC

SENSOR

T2

T2

PRESS FOR

1 SECOND

ON/OFF

T2

OUTPUT

T2

Air Conditioning Basics

The Evaporator, Condenser, Restrictor
(Throttling valve) and Compressor are the four
basic components of an air conditioner. Following
one pound of refrigerant through the system shows
the function of each component.

Subcooled liquid refrigerant at high pressure
enters the restrictor and is throttled to saturated
refrigerant at a lower pressure. The restrictor can be
of either a fixed or TXV/EXV type. The fixed type
must be charged to a target superheat that varies
with indoor and outdoor conditions. TXV/EXV sys­tems must be charged to subcooling.

The evaporator capacity varies with the indoor
heat load on a fixed restrictor. The TXV/EXV regu­lates the size of the restriction to maintain a con­stant superheat. This essentially adjusts the capac­ity of the evaporator responding to the indoor heat
load.

After the restrictor, refrigerant enters the evapo­rator at a low temperature and pressure and boils
(evaporates) into a gas by absorbing heat from the
indoor air. The refrigerant stays at the same tem­perature and pressure until all the refrigerant evap­orates into a gas. After the refrigerant becomes a
gas, it will continue to absorb heat and become
superheated at which point its temperature will
change. The Superheat measurement is the best
indication of refrigerant charge level in a fixed
restrictor system. A TXV/EXV system will keep the

superheat constant. There must be superheat pres­ent to ensure liquid does not flood the compressor.

Superheat measurements are taken on the suc-

tion line between the evaporator and compressor.

The compressor takes this low temperature, low
pressure, slightly superheated refrigerant and com­presses it to a much higher temperature and pres­sure.

The highly superheated gas enters the condens­er and rejects heat into the outside air. The refriger­ant condenses back into a liquid. Once all of the gas
is condensed into a liquid, additional removal of
heat causes a temperature drop that is known as
subcooling. TXV/EXV systems are charged to sub­cooling since superheat is controlled by the throttle
valve. Subcooling measurements are taken on the
liquid line between the condenser and TXV/EXV.
Finally, the subcooled liquid enters the restrictor
and the cycle starts again.

Specifications:

Operating temperature: 0 to 122°F (-18 to 50°C)

at <75%RH

Storage Temperature: -4 to 140°F (-20 to 60°C) 0

to 80%RH with battery removed.

Low battery indication: The is displayed when

the battery drops below the operating level.

Battery Life: Approx. 150 hours (9V alkaline)
Auto Power Off: After 15 minutes of non-usage.
Temperature (K-Type Thermocouple):
Range: -58 to 1832°F (-50 to 1000°C)
Accuracy: ±1°F 50 to 113°F (±0.5°C 10 to 45°C),

when calibrated to NTC at room temperature
±(0.1% rdg+2°F) -58 to 1832°F
±(0.1% rdg+1°C) -50 to 1000°C

Temperature (NTC):
Range: 32 to 140°F (0 to 60°C)
Accuracy:

±1°F 50 to 113°F (±0.5°C 10 to 45°C)
±4°F 32 to 50°F and 113 to 140°F
±2°C 0 to 10°C and 45 to 60°C

Relative Humidity: 0% to 100% RH range
Accuracy: ±2.5% at 77°F (25°C), 10% to 90%RH

±5% at 77°F (25°C) 0 to 10% RH & 90 to 100%RH
Dimensions: 7.9”(20cm) x 2.6”(6.6cm) x

1.4”(3.6cm)

Weight: Approx. 11oz with battery installed
Accessories: (ATA1) K-type dry bulb thermocou-

ple w/ clip, (ATWB1) K-type wet bulb thermo-

couple w/ clip, battery and Operator’s Manual.

Warranty and Service

The product is warranted to the original purchas­er against defects in material or workmanship for a
period of one (1) year from the date of purchase.
During the warranty period, Fieldpiece Instruments
will, at its option, replace or repair the defective unit.

This warranty does not apply to defects resulting
from abuse, neglect, accident, unauthorized repair,
alteration, or unreasonable use of the instrument.
Any implied warranty arising out of the sale of
Fieldpiece’s products including but not limited to
implied warranties of merchantability and fitness for
purpose are limited to the above. Fieldpiece shall
not be liable for incidental or consequential dam­ages.

Return any defective SRH2 to Fieldpiece for
warranty service along with proof of purchase.
Contact Fieldpiece for out of warranty repair
charges.

v28

Auto Power Off, to
disable/recactivate,
hold MAX/MIN/HOLD
button while turning on
SRH2

Low battery
indicator

Relative humidity, dew point, wet bulb, or dry
bulb being measured and displayed on upper
display, press the RH/DP/WB/DB to change

Shows which sensor is being used,
Press SENSOR button to choose

Upper display shows
measurements

Lower display shows
calculated Target
Superheat and Target
Evaporator Exit Temp

Press TSH/TEET/NORM
button to change between
Target Superheat, Exit
Temperature and Normal
Psychrometer mode.

Toggle displays MAX MIN,
HOLD or measure in real-time
by pressing the MAX/MIN/H
button

Outdoor

Indoor

Direction

A-Coil

Filter

Fan

Dry Bulb and
Wet Bulb T/C

Dry Bulb T/C

Supply Plenum

PRESS FOR
1 SECOND

BATTERY
CHECK

AUTO-OFF

Figure 3

Figure 2

Figure 1

WARNING

If creating a hole in the return or supply
plenum is necessary to take accurate measure­ments, make sure you do not damage any equip­ment.

Plug any hole that may have been created in
the supply or return plenum with an air-tight,
long-lasting plug.

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