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The following information is provided for customers interested in calibrating the TRH-100 Probe with their own humidity calibration equipment. Under typical use in controlled residential and commercial indoor environments, the TRH-100 Probe should not require re-calibration for 5+ years.
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.
Re-Calibration (to be performed only if required, typically after a long interval (years) of use)
The Low / High scaling values for the TRH-100 represent the equivalent %RH values at 0v and at 5v. Because the TRH-100's output is nominally 0.9v at 0%RH and 3.9v at 100% RH, the equivalent %RH at 0v (the TRH-100's Low scaling value) will be a negative number, and equivalent %RH at 5v will be a number above 100 (the TRH-100's High scaling value).
In order to perform a re-calibration of the TRH-100, the probe must be placed in an environment (humidity chamber) with a precisely known humidity and stable temperature near room temperature (25°C). Read and note the output voltage of the TRH-100 at a precise low RH environment, and at a precise high RH environment. (For example, read the TRH-100's output voltage at 20%RH and 70%RH). Then using these two Voltage vs %RH readings apply the following formulas:
Y2 = High %RH value, X2 = voltage output at High %RH
Y1 = Low %RH value, X1 = voltage output at Low %RH
Slope m = (Y2 - Y1) / (X2 - X1)
Offset b = Y1 - (m)X1
Low Scaling value = -b/m
High Scaling value = (5 - b)/m
Example:
At 20% RH, TRH-100 output voltage reads 1.6v
At 70% RH, TRH-100 output voltage reads 3.1v
Slope m = (3.1 - 1.6)/(70 - 20) = 0.03
Offset b = 1.6 - (0.03 * 30) = 1.0
New Low Scaling value = -b/m = -1/0.03 = -33.3
New High Scaling value = (5 - b)/m = (5 - 1)/0.03 = 133.33
Note: for customers using an XR440 with the TRH-100, the TRH-100 output voltage can be read by changing the XR440 scaling for the RH channel to a Low value of 0 and a High value of 5. This will cause the XR440 to read the TRH-100's humidity signal in volts.
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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