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The following information is provided especially for customers interested in using the TRH-100 Probe with their own data acquisition equipment. The following information is not needed if you are using the TRH-100 with a Pace Data Logger.
The TRH-100 Probe requires 5 vdc excitation at 2 ma max.
Warm-up time (the time from when 5 vdc power is applied until the humidity output signal is stable) is 100 ms.
The probe has four 24 awg insulated leads with the following colors and functions:
| Black | Signal return (ground) |
| White | 5 vdc excitation |
| Green | Humidity output signal |
| Yellow (or Red) | 30k ohm Thermistor |
CAUTION! The TRH-100 Probe does not have a reverse blocking diode. Double check your connections before applying power! When connecting the probe to live power, first connect the black wire to ground and the white wire to 5v power, and then connect the yellow and green wires to your data acquisition system's inputs. Reversing the power and ground leads will destroy the probe. The Pace XR440 Data Logger (the device the TRH-100 probe was originally designed for) pulses current-limited power to the TRH-100 which prevents damage to the probe if it is incorrectly wired.
The Humidity output signal is approximately 0.9 vdc at 0% RH and 3.9 vdc at 100%RH. Each TRH-100 probe ships with individual scaling values typed on a durable label bonded to the probe's cable. The scaling values are valid for a 0-5v input channel. Convert the output voltage into %RH using these linear scaling values for ±2% RH accuracy from 0-95% RH. The first scaling value is a negative value and represents the equivalent % RH at 0v, the second number represents the equivalent % RH at 5v.
Method 1: Converting the TRH-100's output voltage to %RH using its Low / High scaling values
Use the following formula where:
Vout = output voltage of TRH-100 (green wire)
%RH = (Vout / 5) * (High value - Low value) + Low Value
Example:
TRH-100's output reads 3.1v, Low Value = -33.33, High Value = 133.33
%RH = (3.1 / 5) * (133.33 - (-33.33)) + -33.33 = (0.62 * 166.66) + -33.33 = 103.33 + -33.33 = 70.0
Method 2: Converting the TRH-100's output voltage to %RH using Slope / Offset scaling values
Slope = (High Value - Low Value) / 5
Offset = Low Value
%RH = (Slope * V) + Offset
Where V is the output voltage of the TRH-100
Example:
TRH-100's scaling values: Low = -33.33, High = 133.33, TRH-100's output = 3.1v
Slope = (133.33 - (-33.33)) / 5 = 166.66 / 5 = 33.33
Offset = Low Value = -33.33
%RH = (33.33 * 3.1) + (-33.33) = 70
TRH-100's Temperature Signal
The Thermistor output signal is a resistance which varies precisely with temperature. A resistance vs temperature table for this thermistor is found in the file 'C.rvt' which can be downloaded and unzipped here. The same file is also in Pocket Logger Software's main directory, which is a free download and easy to install (just double click the file). The table is in whole degree C increments. For best accuracy a linear interpolation of the calculated resistance should be performed using the two nearest resistance vs temperature pairs in the table.
Temperature Compensation
The RH output signal should be temperature compensated. This compensation is performed automatically by the PACE Pocket Logger Software. If you are not connecting the TRH-100 to a PACE Pocket Logger, use the following formula:
RHc = RH/(1.0546 - 0.00216 * T)
Definitions:
RH = %RH (not temperature compensated).
T = Temperature of TRH-100's temperature sensor in deg. C.
RHc = %RH (compensated for TRH-100 Probe temperature).
Note: Compensation is negligible (<1%RH) in typical conditioned office environments.
Installation
In moist environments, the TRH-100 Probe should be mounted with the stainless steel filter pointing down. This is to allow any water condensate to drain out the sensor and not collect inside the sensor where it could damage the electronic circuitry within the body of the probe.
Re-Calibration (recommended only if required after a years of use)
Catalog and Price List PDF: 2 MB / 15 pages 
Tel: (704) 799-0688 / Fax: (704) 799-0177 / e-mail: sales@pace-sci.com
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